Network Working Group D. Farinacci
Internet-Draft V. Fuller
Intended status: Experimental D. Meyer
Expires: October 27, 2010 D. Lewis
cisco Systems
April 25, 2010
Locator/ID Separation Protocol (LISP)draft-ietf-lisp-07
Abstract
This draft describes a simple, incremental, network-based protocol to
implement separation of Internet addresses into Endpoint Identifiers
(EIDs) and Routing Locators (RLOCs). This mechanism requires no
changes to host stacks and no major changes to existing database
infrastructures. The proposed protocol can be implemented in a
relatively small number of routers.
This proposal was stimulated by the problem statement effort at the
Amsterdam IAB Routing and Addressing Workshop (RAWS), which took
place in October 2006.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on October 27, 2010.
Copyright Notice
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Internet-Draft Locator/ID Separation Protocol (LISP) April 20102. Introduction
Many years of discussion about the current IP routing and addressing
architecture have noted that its use of a single numbering space (the
"IP address") for both host transport session identification and
network routing creates scaling issues (see [CHIAPPA] and [RFC1498]).
A number of scaling benefits would be realized by separating the
current IP address into separate spaces for Endpoint Identifiers
(EIDs) and Routing Locators (RLOCs); among them are:
1. Reduction of routing table size in the "default-free zone" (DFZ).
Use of a separate numbering space for RLOCs will allow them to be
assigned topologically (in today's Internet, RLOCs would be
assigned by providers at client network attachment points),
greatly improving aggregation and reducing the number of
globally-visible, routable prefixes.
2. More cost-effective multihoming for sites that connect to
different service providers where they can control their own
policies for packet flow into the site without using extra
routing table resources of core routers.
3. Easing of renumbering burden when clients change providers.
Because host EIDs are numbered from a separate, non-provider-
assigned and non-topologically-bound space, they do not need to
be renumbered when a client site changes its attachment points to
the network.
4. Traffic engineering capabilities that can be performed by network
elements and do not depend on injecting additional state into the
routing system. This will fall out of the mechanism that is used
to implement the EID/RLOC split (see Section 4).
5. Mobility without address changing. Existing mobility mechanisms
will be able to work in a locator/ID separation scenario. It
will be possible for a host (or a collection of hosts) to move to
a different point in the network topology either retaining its
home-based address or acquiring a new address based on the new
network location. A new network location could be a physically
different point in the network topology or the same physical
point of the topology with a different provider.
This draft describes protocol mechanisms to achieve the desired
functional separation. For flexibility, the mechanism used for
forwarding packets is decoupled from that used to determine EID to
RLOC mappings. This document covers the former. For the latter, see
[CONS], [ALT], [EMACS], [RPMD], and [NERD]. This work is in response
to and intended to address the problem statement that came out of the
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RAWS effort [RFC4984].
The Routing and Addressing problem statement can be found in [RADIR].
This draft focuses on a router-based solution. Building the solution
into the network will facilitate incremental deployment of the
technology on the Internet. Note that while the detailed protocol
specification and examples in this document assume IP version 4
(IPv4), there is nothing in the design that precludes use of the same
techniques and mechanisms for IPv6. It should be possible for IPv4
packets to use IPv6 RLOCs and for IPv6 EIDs to be mapped to IPv4
RLOCs.
Related work on host-based solutions is described in Shim6 [RFC5533]
and HIP [RFC4423]. Related work on a router-based solution is
described in [GSE]. This draft attempts to not compete or overlap
with such solutions and the proposed protocol changes are expected to
complement a host-based mechanism when Traffic Engineering
functionality is desired.
Some of the design goals of this proposal include:
1. Require no hardware or software changes to end-systems (hosts).
2. Minimize required changes to Internet infrastructure.
3. Be incrementally deployable.
4. Require no router hardware changes.
5. Minimize the number of routers which have to be modified. In
particular, most customer site routers and no core routers
require changes.
6. Minimize router software changes in those routers which are
affected.
7. Avoid or minimize packet loss when EID-to-RLOC mappings need to
be performed.
There are 4 variants of LISP, which differ along a spectrum of strong
to weak dependence on the topological nature and possible need for
routability of EIDs. The variants are:
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LISP 1: uses EIDs that are routable through the RLOC topology for
bootstrapping EID-to-RLOC mappings. [LISP1] This was intended as
a prototyping mechanism for early protocol implementation. It is
now deprecated and SHOULD NOT be deployed.
LISP 1.5: uses EIDs that are routable for bootstrapping EID-to-RLOC
mappings; such routing is via a separate topology.
LISP 2: uses EIDS that are not routable and EID-to-RLOC mappings are
implemented within the DNS. [LISP2]
LISP 3: uses non-routable EIDs that are used as lookup keys for a
new EID-to-RLOC mapping database. Use of Distributed Hash Tables
[DHTs] [LISPDHT] to implement such a database would be an area to
explore. Other examples of new mapping database services are
[CONS], [ALT], [RPMD], [NERD], and [APT].
This document on LISP 1.5, and LISP 3 variants, both of which rely on
a router-based distributed cache and database for EID-to-RLOC
mappings. The LISP 1.0 mechanism works but does not allow reduction
of routing information in the default-free-zone of the Internet. The
LISP 2 mechanisms are put on hold and may never come to fruition
since it is not architecturally pure to have routing depend on
directory and directory depend on routing. The LISP 3 mechanisms
will be documented elsewhere but may use the control-plane options
specified in this specification.
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Internet-Draft Locator/ID Separation Protocol (LISP) April 20103. Definition of Terms
Provider Independent (PI) Addresses: an address block assigned from
a pool where blocks are not associated with any particular
location in the network (e.g. from a particular service provider),
and is therefore not topologically aggregatable in the routing
system.
Provider Assigned (PA) Addresses: a block of IP addresses that are
assigned to a site by each service provider to which a site
connects. Typically, each block is sub-block of a service
provider CIDR block and is aggregated into the larger block before
being advertised into the global Internet. Traditionally, IP
multihoming has been implemented by each multi-homed site
acquiring its own, globally-visible prefix. LISP uses only
topologically-assigned and aggregatable address blocks for RLOCs,
eliminating this demonstrably non-scalable practice.
Routing Locator (RLOC): the IPv4 or IPv6 address of an egress
tunnel router (ETR). It is the output of a EID-to-RLOC mapping
lookup. An EID maps to one or more RLOCs. Typically, RLOCs are
numbered from topologically-aggregatable blocks that are assigned
to a site at each point to which it attaches to the global
Internet; where the topology is defined by the connectivity of
provider networks, RLOCs can be thought of as PA addresses.
Multiple RLOCs can be assigned to the same ETR device or to
multiple ETR devices at a site.
Endpoint ID (EID): a 32-bit (for IPv4) or 128-bit (for IPv6) value
used in the source and destination address fields of the first
(most inner) LISP header of a packet. The host obtains a
destination EID the same way it obtains an destination address
today, for example through a DNS lookup or SIP exchange. The
source EID is obtained via existing mechanisms used to set a
host's "local" IP address. An EID is allocated to a host from an
EID-prefix block associated with the site where the host is
located. An EID can be used by a host to refer to other hosts.
EIDs MUST NOT be used as LISP RLOCs. Note that EID blocks may be
assigned in a hierarchical manner, independent of the network
topology, to facilitate scaling of the mapping database. In
addition, an EID block assigned to a site may have site-local
structure (subnetting) for routing within the site; this structure
is not visible to the global routing system. When used in
discussions with other Locator/ID separation proposals, a LISP EID
will be called a "LEID". Throughout this document, any references
to "EID" refers to an LEID.
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EID-prefix: A power-of-2 block of EIDs which are allocated to a
site by an address allocation authority. EID-prefixes are
associated with a set of RLOC addresses which make up a "database
mapping". EID-prefix allocations can be broken up into smaller
blocks when an RLOC set is to be associated with the smaller EID-
prefix. A globally routed address block (whether PI or PA) is not
an EID-prefix. However, a globally routed address block may be
removed from global routing and reused as an EID-prefix. A site
that receives an explicitly allocated EID-prefix may not use that
EID-prefix as a globally routed prefix assigned to RLOCs.
End-system: is an IPv4 or IPv6 device that originates packets with
a single IPv4 or IPv6 header. The end-system supplies an EID
value for the destination address field of the IP header when
communicating globally (i.e. outside of its routing domain). An
end-system can be a host computer, a switch or router device, or
any network appliance.
Ingress Tunnel Router (ITR): a router which accepts an IP packet
with a single IP header (more precisely, an IP packet that does
not contain a LISP header). The router treats this "inner" IP
destination address as an EID and performs an EID-to-RLOC mapping
lookup. The router then prepends an "outer" IP header with one of
its globally-routable RLOCs in the source address field and the
result of the mapping lookup in the destination address field.
Note that this destination RLOC may be an intermediate, proxy
device that has better knowledge of the EID-to-RLOC mapping closer
to the destination EID. In general, an ITR receives IP packets
from site end-systems on one side and sends LISP-encapsulated IP
packets toward the Internet on the other side.
Specifically, when a service provider prepends a LISP header for
Traffic Engineering purposes, the router that does this is also
regarded as an ITR. The outer RLOC the ISP ITR uses can be based
on the outer destination address (the originating ITR's supplied
RLOC) or the inner destination address (the originating hosts
supplied EID).
TE-ITR: is an ITR that is deployed in a service provider network
that prepends an additional LISP header for Traffic Engineering
purposes.
Egress Tunnel Router (ETR): a router that accepts an IP packet
where the destination address in the "outer" IP header is one of
its own RLOCs. The router strips the "outer" header and forwards
the packet based on the next IP header found. In general, an ETR
receives LISP-encapsulated IP packets from the Internet on one
side and sends decapsulated IP packets to site end-systems on the
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other side. ETR functionality does not have to be limited to a
router device. A server host can be the endpoint of a LISP tunnel
as well.
TE-ETR: is an ETR that is deployed in a service provider network
that strips an outer LISP header for Traffic Engineering purposes.
xTR: is a reference to an ITR or ETR when direction of data flow is
not part of the context description. xTR refers to the router that
is the tunnel endpoint. Used synonymously with the term "Tunnel
Router". For example, "An xTR can be located at the Customer Edge
(CE) router", meaning both ITR and ETR functionality is at the CE
router.
EID-to-RLOC Cache: a short-lived, on-demand table in an ITR that
stores, tracks, and is responsible for timing-out and otherwise
validating EID-to-RLOC mappings. This cache is distinct from the
full "database" of EID-to-RLOC mappings, it is dynamic, local to
the ITR(s), and relatively small while the database is
distributed, relatively static, and much more global in scope.
EID-to-RLOC Database: a global distributed database that contains
all known EID-prefix to RLOC mappings. Each potential ETR
typically contains a small piece of the database: the EID-to-RLOC
mappings for the EID prefixes "behind" the router. These map to
one of the router's own, globally-visible, IP addresses. The same
database mapping entries MUST be configured on all ETRs for a
given site. That is, the EID-prefixes for the site and locator-
set for each EID-prefix MUST be the same on all ETRs so they
consistently send Map-Reply messages with the same database
mapping contents.
Recursive Tunneling: when a packet has more than one LISP IP
header. Additional layers of tunneling may be employed to
implement traffic engineering or other re-routing as needed. When
this is done, an additional "outer" LISP header is added and the
original RLOCs are preserved in the "inner" header. Any
references to tunnels in this specification refers to dynamic
encapsulating tunnels and never are they statically configured.
Reencapsulating Tunnels: when a packet has no more than one LISP IP
header (two IP headers total) and when it needs to be diverted to
new RLOC, an ETR can decapsulate the packet (remove the LISP
header) and prepends a new tunnel header, with new RLOC, on to the
packet. Doing this allows a packet to be re-routed by the re-
encapsulating router without adding the overhead of additional
tunnel headers. Any references to tunnels in this specification
refers to dynamic encapsulating tunnels and never are they
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statically configured.
LISP Header: a term used in this document to refer to the outer
IPv4 or IPv6 header, a UDP header, and a LISP-specific 8-byte
header that follows the UDP header, an ITR prepends or an ETR
strips.
Address Family Identifier (AFI): a term used to describe an address
encoding in a packet. An address family currently pertains to an
IPv4 or IPv6 address. See [AFI] and [RFC1700] for details. An
AFI value of 0 used in this specification indicates an unspecified
encoded address where the the length of the address is 0 bytes
following the 16-bit AFI value of 0.
Negative Mapping Entry: also known as a negative cache entry, is an
EID-to-RLOC entry where an EID-prefix is advertised or stored with
no RLOCs. That is, the locator-set for the EID-to-RLOC entry is
empty or has an encoded locator count of 0. This type of entry
could be used to describe a prefix from a non-LISP site, which is
explicitly not in the mapping database. There are a set of well
defined actions that are encoded in a Negative Map-Reply.
Data Probe: a LISP-encapsulated data packet where the inner header
destination address equals the outer header destination address
used to trigger a Map-Reply by a decapsulating ETR. In addition,
the original packet is decapsulated and delivered to the
destination host. A Data Probe is used in some of the mapping
database designs to "probe" or request a Map-Reply from an ETR; in
other cases, Map-Requests are used. See each mapping database
design for details.
Proxy ITR (PITR): also known as a PTR is defined and described in
[INTERWORK], a PITR acts like an ITR but does so on behalf of non-
LISP sites which send packets to destinations at LISP sites.
Proxy ETR (PETR): is defined and described in [INTERWORK], a PETR
acts like an ETR but does so on behalf of LISP sites which send
packets to destinations at non-LISP sites.
Route-returnability: is an assumption that the underlying routing
system will deliver packets to the destination. When combined
with a nonce that is provided by a sender and returned by a
receiver limits off-path data insertion.
LISP site: is a set of routers in an edge network that are under a
single technical administration. LISP routers which reside in the
edge network are the demarcation points to separate the edge
network from the core network.
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Internet-Draft Locator/ID Separation Protocol (LISP) April 20104. Basic Overview
One key concept of LISP is that end-systems (hosts) operate the same
way they do today. The IP addresses that hosts use for tracking
sockets, connections, and for sending and receiving packets do not
change. In LISP terminology, these IP addresses are called Endpoint
Identifiers (EIDs).
Routers continue to forward packets based on IP destination
addresses. When a packet is LISP encapsulated, these addresses are
referred to as Routing Locators (RLOCs). Most routers along a path
between two hosts will not change; they continue to perform routing/
forwarding lookups on the destination addresses. For routers between
the source host and the ITR as well as routers from the ETR to the
destination host, the destination address is an EID. For the routers
between the ITR and the ETR, the destination address is an RLOC.
This design introduces "Tunnel Routers", which prepends LISP headers
on host-originated packets and strip them prior to final delivery to
their destination. The IP addresses in this "outer header" are
RLOCs. During end-to-end packet exchange between two Internet hosts,
an ITR prepends a new LISP header to each packet and an egress tunnel
router strips the new header. The ITR performs EID-to-RLOC lookups
to determine the routing path to the the ETR, which has the RLOC as
one of its IP addresses.
Some basic rules governing LISP are:
o End-systems (hosts) only send to addresses which are EIDs. They
don't know addresses are EIDs versus RLOCs but assume packets get
to LISP routers, which in turn, deliver packets to the destination
the end-system has specified.
o EIDs are always IP addresses assigned to hosts.
o LISP routers mostly deal with Routing Locator addresses. See
details later in Section 4.1 to clarify what is meant by "mostly".
o RLOCs are always IP addresses assigned to routers; preferably,
topologically-oriented addresses from provider CIDR blocks.
o When a router originates packets it may use as a source address
either an EID or RLOC. When acting as a host (e.g. when
terminating a transport session such as SSH, TELNET, or SNMP), it
may use an EID that is explicitly assigned for that purpose. An
EID that identifies the router as a host MUST NOT be used as an
RLOC; an EID is only routable within the scope of a site. A
typical BGP configuration might demonstrate this "hybrid" EID/RLOC
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usage where a router could use its "host-like" EID to terminate
iBGP sessions to other routers in a site while at the same time
using RLOCs to terminate eBGP sessions to routers outside the
site.
o EIDs are not expected to be usable for global end-to-end
communication in the absence of an EID-to-RLOC mapping operation.
They are expected to be used locally for intra-site communication.
o EID prefixes are likely to be hierarchically assigned in a manner
which is optimized for administrative convenience and to
facilitate scaling of the EID-to-RLOC mapping database. The
hierarchy is based on a address allocation hierarchy which is not
dependent on the network topology.
o EIDs may also be structured (subnetted) in a manner suitable for
local routing within an autonomous system.
An additional LISP header may be prepended to packets by a transit
router (i.e. TE-ITR) when re-routing of the path for a packet is
desired. An obvious instance of this would be an ISP router that
needs to perform traffic engineering for packets flowing through its
network. In such a situation, termed Recursive Tunneling, an ISP
transit acts as an additional ingress tunnel router and the RLOC it
uses for the new prepended header would be either a TE-ETR within the
ISP (along intra-ISP traffic engineered path) or a TE-ETR within
another ISP (an inter-ISP traffic engineered path, where an agreement
to build such a path exists).
This specification mandates that no more than two LISP headers get
prepended to a packet. This avoids excessive packet overhead as well
as possible encapsulation loops. It is believed two headers is
sufficient, where the first prepended header is used at a site for
Location/Identity separation and second prepended header is used
inside a service provider for Traffic Engineering purposes.
Tunnel Routers can be placed fairly flexibly in a multi-AS topology.
For example, the ITR for a particular end-to-end packet exchange
might be the first-hop or default router within a site for the source
host. Similarly, the egress tunnel router might be the last-hop
router directly-connected to the destination host. Another example,
perhaps for a VPN service out-sourced to an ISP by a site, the ITR
could be the site's border router at the service provider attachment
point. Mixing and matching of site-operated, ISP-operated, and other
tunnel routers is allowed for maximum flexibility. See Section 8 for
more details.
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Internet-Draft Locator/ID Separation Protocol (LISP) April 20104.1. Packet Flow Sequence
This section provides an example of the unicast packet flow with the
following conditions:
o Source host "host1.abc.com" is sending a packet to
"host2.xyz.com", exactly what host1 would do if the site was not
using LISP.
o Each site is multi-homed, so each tunnel router has an address
(RLOC) assigned from the service provider address block for each
provider to which that particular tunnel router is attached.
o The ITR(s) and ETR(s) are directly connected to the source and
destination, respectively, but the source and destination can be
located anywhere in LISP site.
o Map-Requests can be sent on the underlying routing system topology
(LISP 1.0) or over an alternative topology [ALT].
o Map-Replies are sent on the underlying routing system topology.
Client host1.abc.com wants to communicate with server host2.xyz.com:
1. host1.abc.com wants to open a TCP connection to host2.xyz.com.
It does a DNS lookup on host2.xyz.com. An A/AAAA record is
returned. This address is the destination EID. The locally-
assigned address of host1.abc.com is used as the source EID. An
IPv4 or IPv6 packet is built and forwarded through the LISP site
as a normal IP packet until it reaches a LISP ITR.
2. The LISP ITR must be able to map the EID destination to an RLOC
of one of the ETRs at the destination site. The specific method
used to do this is not described in this example. See [ALT] or
[CONS] for possible solutions.
3. The ITR will send a LISP Map-Request. Map-Requests SHOULD be
rate-limited.
4. In LISP 1.0, the Map-Request packet is routed through the
underlying routing system. In LISP 1.5, the Map-Request packet
is routed on an alternate logical topology. In either case, when
the Map-Request arrives at one of the ETRs at the destination
site, it will process the packet as a control message.
5. The ETR looks at the destination EID of the Map-Request and
matches it against the prefixes in the ETR's configured EID-to-
RLOC mapping database. This is the list of EID-prefixes the ETR
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is supporting for the site it resides in. If there is no match,
the Map-Request is dropped. Otherwise, a LISP Map-Reply is
returned to the ITR.
6. The ITR receives the Map-Reply message, parses the message (to
check for format validity) and stores the mapping information
from the packet. This information is put in the ITR's EID-to-
RLOC mapping cache (this is the on-demand cache, the cache where
entries time out due to inactivity).
7. Subsequent packets from host1.abc.com to host2.xyz.com will have
a LISP header prepended by the ITR using the appropriate RLOC as
the LISP header destination address learned from the ETR. Note,
the packet may be sent to a different ETR than the one which
returned the Map-Reply due to the source site's hashing policy or
the destination site's locator-set policy.
8. The ETR receives these packets directly (since the destination
address is one of its assigned IP addresses), strips the LISP
header and forwards the packets to the attached destination host.
In order to eliminate the need for a mapping lookup in the reverse
direction, an ETR MAY create a cache entry that maps the source EID
(inner header source IP address) to the source RLOC (outer header
source IP address) in a received LISP packet. Such a cache entry is
termed a "gleaned" mapping and only contains a single RLOC for the
EID in question. More complete information about additional RLOCs
SHOULD be verified by sending a LISP Map-Request for that EID. Both
ITR and the ETR may also influence the decision the other makes in
selecting an RLOC. See Section 6 for more details.
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Internet-Draft Locator/ID Separation Protocol (LISP) April 20105. Tunneling Details
This section describes the LISP Data Message which defines the
tunneling header used to encapsulate IPv4 and IPv6 packets which
contain EID addresses. Even though the following formats illustrate
IPv4-in-IPv4 and IPv6-in-IPv6 encapsulations, the other 2
combinations are supported as well.
Since additional tunnel headers are prepended, the packet becomes
larger and in theory can exceed the MTU of any link traversed from
the ITR to the ETR. It is recommended, in IPv4 that packets do not
get fragmented as they are encapsulated by the ITR. Instead, the
packet is dropped and an ICMP Too Big message is returned to the
source.
Based on informal surveys of large ISP traffic patterns, it appears
that most transit paths can accommodate a path MTU of at least 4470
bytes. The exceptions, in terms of data rate, number of hosts
affected, or any other metric are expected to be vanishingly small.
To address MTU concerns, mainly raised on the RRG mailing list, the
LISP deployment process will include collecting data during its pilot
phase to either verify or refute the assumption about minimum
available MTU. If the assumption proves true and transit networks
with links limited to 1500 byte MTUs are corner cases, it would seem
more cost-effective to either upgrade or modify the equipment in
those transit networks to support larger MTUs or to use existing
mechanisms for accommodating packets that are too large.
For this reason, there is currently no plan for LISP to add any new
additional, complex mechanism for implementing fragmentation and
reassembly in the face of limited-MTU transit links. If analysis
during LISP pilot deployment reveals that the assumption of
essentially ubiquitous, 4470+ byte transit path MTUs, is incorrect,
then LISP can be modified prior to protocol standardization to add
support for one of the proposed fragmentation and reassembly schemes.
Note that two simple existing schemes are detailed in Section 5.4.
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r + +
| |
^ + Destination EID +
\ | |
\ + +
\ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.3. Tunnel Header Field Descriptions
Inner Header: is the inner header, preserved from the datagram
received from the originating host. The source and destination IP
addresses are EIDs.
Outer Header: is the outer header prepended by an ITR. The address
fields contain RLOCs obtained from the ingress router's EID-to-
RLOC cache. The IP protocol number is "UDP (17)" from [RFC0768].
The DF bit of the Flags field is set to 0 when the method in
Section 5.4.1 is used and set to 1 when the method in
Section 5.4.2 is used.
UDP Header: contains a ITR selected source port when encapsulating a
packet. See Section 6.4 for details on the hash algorithm used to
select a source port based on the 5-tuple of the inner header.
The destination port MUST be set to the well-known IANA assigned
port value 4341.
UDP Checksum: this field SHOULD be transmitted as zero by an ITR for
either IPv4 [RFC0768] or IPv6 encapsulation [UDP-TUNNELS]. When a
packet with a zero UDP checksum is received by an ETR, the ETR
MUST accept the packet for decapsulation. When an ITR transmits a
non-zero value for the UDP checksum, it MUST send a correctly
computed value in this field. When an ETR receives a packet with
a non-zero UDP checksum, it MAY choose to verify the checksum
value. If it chooses to perform such verification, and the
verification fails, the packet MUST be silently dropped. If the
ETR chooses not to perform the verification, or performs the
verification successfully, the packet MUST be accepted for
decapsulation. The handling of UDP checksums for all tunneling
protocols, including LISP, is under active discussion within the
IETF. When that discussion concludes, any necessary changes will
be made to align LISP with the outcome of the broader discussion.
UDP Length: for an IPv4 encapsulated packet, the inner header Total
Length plus the UDP and LISP header lengths are used. For an IPv6
encapsulated packet, the inner header Payload Length plus the size
of the IPv6 header (40 bytes) plus the size of the UDP and LISP
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headers are used. The UDP header length is 8 bytes.
N: this is the nonce-present bit. When this bit is set to 1, the
low-order 24-bits of the first 32-bits of the LISP header contains
a Nonce. See Section 6.3.1 for details. Both N and V bits MUST
NOT be set in the same packet. If they are, a decapsulating ETR
MUST treat the "Nonce/Map-Version" field as having a Nonce value
present.
L: this is the Locator-Status-Bits field enabled bit. When this bit
is set to 1, the Locator-Status-Bits in the second 32-bits of the
LISP header are in use.
x 1 x x 0 x x x
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N|L|E|V|I|flags| Nonce/Map-Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Locator Status Bits |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
E: this is the echo-nonce-request bit. When this bit is set to 1,
the N bit MUST be 1. This bit SHOULD be ignored and has no
meaning when the N bit is set to 0. See Section 6.3.1 for
details.
V: this is the Map-Version present bit. When this bit is set to 1,
the N bit MUST be 0. Refer to Section 6.5.3 for more details.
This bit indicates that the first 4 bytes of the LISP header is
encoded as:
0 x 0 1 x x x x
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N|L|E|V|I|flags| Source Map-Version | Dest Map-Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Instance ID/Locator Status Bits |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
I: this is the Instance ID bit. See Section 5.5 for more details.
When this bit is set to 1, the Locator Status Bits field is
reduced to 8-bits and the high-order 24-bits are used as an
Instance ID. If the L-bit is set to 0, then the low-order 8 bits
are transmitted as zero and ignored on receipt. The format of the
last 4 bytes of the LISP header would look like:
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x x x x 1 x x x
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N|L|E|V|I|flags| Nonce/Map-Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Instance ID | LSBs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
flags: this 3-bit field is reserved for future flag use. It is set
to 0 on transmit and ignored on receipt.
LISP Nonce: is a 24-bit value that is randomly generated by an ITR
when the N-bit is set to 1. The nonce is also used when the E-bit
is set to request the nonce value to be echoed by the other side
when packets are returned. When the E-bit is clear but the N-bit
is set, a remote ITR is either echoing a previously requested
echo-nonce or providing a random nonce. See Section 6.3.1 for
more details.
LISP Locator Status Bits: in the LISP header are set by an ITR to
indicate to an ETR the up/down status of the Locators in the
source site. Each RLOC in a Map-Reply is assigned an ordinal
value from 0 to n-1 (when there are n RLOCs in a mapping entry).
The Locator Status Bits are numbered from 0 to n-1 from the least
significant bit of field. The field is 32-bits when the I-bit is
set to 0 and is 8 bits when the I-bit is set to 1. When a Locator
Status Bit is set to 1, the ITR is indicating to the ETR the RLOC
associated with the bit ordinal has up status. See Section 6.3
for details on how an ITR can determine the status of other ITRs
at the same site. When a site has multiple EID-prefixes which
result in multiple mappings (where each could have a different
locator-set), the Locator Status Bits setting in an encapsulated
packet MUST reflect the mapping for the EID-prefix that the inner-
header source EID address matches.
When doing Recursive Tunneling or ITR/PTR encapsulation:
o The outer header Time to Live field (or Hop Limit field, in case
of IPv6) SHOULD be copied from the inner header Time to Live
field.
o The outer header Type of Service field (or the Traffic Class
field, in the case of IPv6) SHOULD be copied from the inner header
Type of Service field (with one caveat, see below).
When doing Re-encapsulated Tunneling:
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o The new outer header Time to Live field SHOULD be copied from the
stripped outer header Time to Live field.
o The new outer header Type of Service field SHOULD be copied from
the stripped OH header Type of Service field (with one caveat, see
below).
Copying the TTL serves two purposes: first, it preserves the distance
the host intended the packet to travel; second, and more importantly,
it provides for suppression of looping packets in the event there is
a loop of concatenated tunnels due to misconfiguration.
The ECN field occupies bits 6 and 7 of both the IPv4 Type of Service
field and the IPv6 Traffic Class field [RFC3168]. The ECN field
requires special treatment in order to avoid discarding indications
of congestion [RFC3168]. ITR encapsulation MUST copy the 2-bit ECN
field from the inner header to the outer header. Re-encapsulation
MUST copy the 2-bit ECN field from the stripped outer header to the
new outer header. If the ECN field contains a congestion indication
codepoint (the value is '11', the Congestion Experienced (CE)
codepoint), then ETR decapsulation MUST copy the 2-bit ECN field from
the stripped outer header to the surviving inner header that is used
to forward the packet beyond the ETR. These requirements preserve
Congestion Experienced (CE) indications when a packet that uses ECN
traverses a LISP tunnel and becomes marked with a CE indication due
to congestion between the tunnel endpoints.
5.4. Dealing with Large Encapsulated Packets
In the event that the MTU issues mentioned above prove to be more
serious than expected, this section proposes 2 simple mechanisms to
deal with large packets. One is stateless using IP fragmentation and
the other is stateful using Path MTU Discovery [RFC1191].
It is left to the implementor to decide if the stateless or stateful
mechanism SHOULD be implemented. Both or neither can be decided as
well since it is a local decision in the ITR regarding how to deal
with MTU issues. Sites can interoperate with differing mechanisms.
Both stateless and stateful mechanisms also apply to Reencapsulating
and Recursive Tunneling. So any actions below referring to an ITR
also apply to an TE-ITR.
5.4.1. A Stateless Solution to MTU Handling
An ITR stateless solution to handle MTU issues is described as
follows:
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1. Define an architectural constant S for the maximum size of a
packet, in bytes, an ITR would receive from a source inside of
its site.
2. Define L to be the maximum size, in bytes, a packet of size S
would be after the ITR prepends the LISP header, UDP header, and
outer network layer header of size H.
3. Calculate: S + H = L.
When an ITR receives a packet from a site-facing interface and adds H
bytes worth of encapsulation to yield a packet size greater than L
bytes, it resolves the MTU issue by first splitting the original
packet into 2 equal-sized fragments. A LISP header is then prepended
to each fragment. This will ensure that the new, encapsulated
packets are of size (S/2 + H), which is always below the effective
tunnel MTU.
When an ETR receives encapsulated fragments, it treats them as two
individually encapsulated packets. It strips the LISP headers then
forwards each fragment to the destination host of the destination
site. The two fragments are reassembled at the destination host into
the single IP datagram that was originated by the source host.
This behavior is performed by the ITR when the source host originates
a packet with the DF field of the IP header is set to 0. When the DF
field of the IP header is set to 1, or the packet is an IPv6 packet
originated by the source host, the ITR will drop the packet when the
size is greater than L, and sends an ICMP Too Big message to the
source with a value of S, where S is (L - H).
When the outer header encapsulation uses an IPv4 header, an
implementation SHOULD set the DF bit to 1 so ETR fragment reassembly
can be avoided. An implementation MAY set the DF bit in such headers
to 0 if it has good reason to believe there are unresolvable path MTU
issues between the sending ITR and the receiving ETR.
This specification recommends that L be defined as 1500.
5.4.2. A Stateful Solution to MTU Handling
An ITR stateful solution to handle MTU issues is described as follows
and was first introduced in [OPENLISP]:
1. The ITR will keep state of the effective MTU for each locator per
mapping cache entry. The effective MTU is what the core network
can deliver along the path between ITR and ETR.
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2. When an IPv6 encapsulated packet or an IPv4 encapsulated packet
with DF bit set to 1, exceeds what the core network can deliver,
one of the intermediate routers on the path will send an ICMP Too
Big message to the ITR. The ITR will parse the ICMP message to
determine which locator is affected by the effective MTU change
and then record the new effective MTU value in the mapping cache
entry.
3. When a packet is received by the ITR from a source inside of the
site and the size of the packet is greater than the effective MTU
stored with the mapping cache entry associated with the
destination EID the packet is for, the ITR will send an ICMP Too
Big message back to the source. The packet size advertised by
the ITR in the ICMP Too Big message is the effective MTU minus
the LISP encapsulation length.
Even though this mechanism is stateful, it has advantages over the
stateless IP fragmentation mechanism, by not involving the
destination host with reassembly of ITR fragmented packets.
5.5. Using Virtualization and Segmentation with LISP
When multiple organizations inside of a LISP site are using private
addresses [RFC1918] as EID-prefixes, their address spaces MUST remain
segregated due to possible address duplication. An Instance ID in
the address encoding can aid in making the entire AFI based address
unique. See [LCAF] for details for a possible address encoding. The
LCAF encoding is an area for further study.
An Instance ID can be carried in a LISP encapsulated packet. An ITR
that prepends a LISP header, will copy a 24-bit value, used by the
LISP router to uniquely identify the address space. The value is
copied to the Instance ID field of the LISP header and the I-bit is
set to 1.
When an ETR decapsulate a packet, the Instance ID from the LISP
header is used as a table identifier to locate the forwarding table
to use for the inner destination EID lookup.
Some examples of the 24-bit value to copy or map into the Instance ID
field could be a 802.1Q VLAN tag or a configured VRF-ID value.
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| |
+ Destination Routing Locator +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Source Port | Dest Port |
UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | UDP Length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| LISP Message |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The LISP UDP-based messages are the Map-Request and Map-Reply
messages. When a UDP Map-Request is sent, the UDP source port is
chosen by the sender and the destination UDP port number is set to
4342. When a UDP Map-Reply is sent, the source UDP port number is
set to 4342 and the destination UDP port number is copied from the
source port of either the Map-Request or the invoking data packet.
The UDP Length field will reflect the length of the UDP header and
the LISP Message payload.
The UDP Checksum is computed and set to non-zero for Map-Request,
Map-Reply, Map-Register and ECM control messages. It MUST be checked
on receipt and if the checksum fails, the packet MUST be dropped.
LISP-CONS [CONS] use TCP to send LISP control messages. The format
of control messages includes the UDP header so the checksum and
length fields can be used to protect and delimit message boundaries.
This main LISP specification is the authoritative source for message
format definitions for the Map-Request and Map-Reply messages.
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Type: 1 (Map-Request)
A: This is an authoritative bit, which is set to 0 for UDP-based Map-
Requests sent by an ITR.
M: When set, it indicates a Map-Reply Record segment is included in
the Map-Request.
P: This is the probe-bit which indicates that a Map-Request SHOULD be
treated as a locator reachability probe. The receiver SHOULD
respond with a Map-Reply with the probe-bit set, indicating the
Map-Reply is a locator reachability probe reply, with the nonce
copied from the Map-Request. See Section 6.3.2 for more details.
S: This is the SMR bit. See Section 6.5.2 for details.
Reserved: Set to 0 on transmission and ignored on receipt.
IRC: This 5-bit field is the ITR-RLOC Count which encodes the number
of (ITR-RLOC-AFI, ITR-RLOC Address) fields present in this
message. Multiple ITR-RLOC Address fields are used so a Map-
Replier can select which destination address to use for a Map-
Reply. The IRC value ranges from 0 to 31, where IRC value 0 means
an ITR-RLOC address count of 1, an IRC value of 1 means an ITR-
RLOC address count of 2, and so on up to an IRC value of 31, which
means an ITR-RLOC address count of 32.
Record Count: The number of records in this Map-Request message. A
record is comprised of the portion of the packet that is labeled
'Rec' above and occurs the number of times equal to Record Count.
For this version of the protocol, a receiver MUST accept and
process Map-Requests that contain one or more records, but a
sender MUST only send Map-Requests containing one record. Support
for requesting multiple EIDs in a single Map-Request message will
be specified in a future version of the protocol.
Nonce: An 8-byte random value created by the sender of the Map-
Request. This nonce will be returned in the Map-Reply. The
security of the LISP mapping protocol depends critically on the
strength of the nonce in the Map-Request message. The nonce
SHOULD be generated by a properly seeded pseudo-random (or strong
random) source. See [RFC4086] for advice on generating security-
sensitive random data.
Source-EID-AFI: Address family of the "Source EID Address" field.
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Source EID Address: This is the EID of the source host which
originated the packet which is invoking this Map-Request. When
Map-Requests are used for refreshing a map-cache entry or for
RLOC-probing, the value 0 is used.
ITR-RLOC-AFI: Address family of the "ITR-RLOC Address" field that
follows this field.
ITR-RLOC Address: Used to give the ETR the option of selecting the
destination address from any address family for the Map-Reply
message. This address MUST be a routable RLOC address.
EID mask-len: Mask length for EID prefix.
EID-prefix-AFI: Address family of EID-prefix according to [RFC5226]
EID-prefix: 4 bytes if an IPv4 address-family, 16 bytes if an IPv6
address-family. When a Map-Request is sent by an ITR because a
data packet is received for a destination where there is no
mapping entry, the EID-prefix is set to the destination IP address
of the data packet. And the 'EID mask-len' is set to 32 or 128
for IPv4 or IPv6, respectively. When an xTR wants to query a site
about the status of a mapping it already has cached, the EID-
prefix used in the Map-Request has the same mask-length as the
EID-prefix returned from the site when it sent a Map-Reply
message.
Map-Reply Record: When the M bit is set, this field is the size of
the "Record" field in the Map-Reply format. This Map-Reply record
contains the EID-to-RLOC mapping entry associated with the Source
EID. This allows the ETR which will receive this Map-Request to
cache the data if it chooses to do so.
Mapping Protocol Data: See [CONS] or [ALT] for details. This field
is optional and present when the UDP length indicates there is
enough space in the packet to include it.
6.1.3. EID-to-RLOC UDP Map-Request Message
A Map-Request is sent from an ITR when it needs a mapping for an EID,
wants to test an RLOC for reachability, or wants to refresh a mapping
before TTL expiration. For the initial case, the destination IP
address used for the Map-Request is the destination-EID from the
packet which had a mapping cache lookup failure. For the latter 2
cases, the destination IP address used for the Map-Request is one of
the RLOC addresses from the locator-set of the map cache entry. The
source address is either an IPv4 or IPv6 RLOC address depending if
the Map-Request is using an IPv4 versus IPv6 header, respectively.
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In all cases, the UDP source port number for the Map-Request message
is a randomly allocated 16-bit value and the UDP destination port
number is set to the well-known destination port number 4342. A
successful Map-Reply updates the cached set of RLOCs associated with
the EID prefix range.
One or more Map-Request (ITR-RLOC-AFI, ITR-RLOC-Address) fields MUST
be filled in by the ITR. The number of fields (minus 1) encoded MUST
be placed in the IRC field. The ITR MAY include all locally
configured locators in this list or just provide one locator address
from each address family it supports. If the ITR erroneously
provides no ITR-RLOC addresses, the Map-Replier MUST drop the Map-
Request.
Map-Requests can also be LISP encapsulated using UDP destination port
4342 with a LISP type value set to "Encapsulated Control Message",
when sent from an ITR to a Map-Resolver. Likewise, Map-Requests are
LISP encapsulated the same way from a Map-Server to an ETR. Details
on encapsulated Map-Requests and Map-Resolvers can be found in
[LISP-MS].
Map-Requests MUST be rate-limited. It is recommended that a Map-
Request for the same EID-prefix be sent no more than once per second.
An ITR that is configured with mapping database information (i.e. it
is also an ETR) may optionally include those mappings in a Map-
Request. When an ETR configured to accept and verify such
"piggybacked" mapping data receives such a Map-Request and it does
not have this mapping in the map-cache, it may originate a "verifying
Map-Request", addressed to the map-requesting ITR. If the ETR has a
map-cache entry that matches the "piggybacked" EID and the RLOC is in
the locator-set for the entry, then it may send the "verifying Map-
Request" directly to the originating Map-Request source. If the RLOC
is not in the locator-set, then the ETR MUST send the "verifying Map-
Request" to the "piggybacked" EID. Doing this forces the "verifying
Map-Request" to go through the mapping database system to reach the
authoritative source of information about that EID, guarding against
RLOC-spoofing in in the "piggybacked" mapping data.
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Record Count: The number of records in this reply message. A record
is comprised of that portion of the packet labeled 'Record' above
and occurs the number of times equal to Record count.
Nonce: A 24-bit value set in a Data-Probe packet or a 64-bit value
from the Map-Request is echoed in this Nonce field of the Map-
Reply.
Record TTL: The time in minutes the recipient of the Map-Reply will
store the mapping. If the TTL is 0, the entry SHOULD be removed
from the cache immediately. If the value is 0xffffffff, the
recipient can decide locally how long to store the mapping.
Locator Count: The number of Locator entries. A locator entry
comprises what is labeled above as 'Loc'. The locator count can
be 0 indicating there are no locators for the EID-prefix.
EID mask-len: Mask length for EID prefix.
ACT: This 3-bit field describes negative Map-Reply actions. These
bits are used only when the 'Locator Count' field is set to 0.
The action bits are encoded only in Map-Reply messages. The
actions defined are used by an ITR or PTR when a destination EID
matches a negative mapping cache entry. Unassigned values should
cause a map-cache entry to be created and, when packets match this
negative cache entry, they will be dropped. The current assigned
values are:
(0) Drop: The packet is dropped silently.
(1) Natively-Forward: The packet is not encapsulated or dropped
but natively forwarded.
(2) Send-Map-Request: The packet invokes sending a Map-Request.
A: The Authoritative bit, when sent by a UDP-based message is always
set to 1 by an ETR. See [CONS] for TCP-based Map-Replies. When a
Map-Server is proxy Map-Replying [LISP-MS] for a LISP site, the
Authoritative bit is set to 0. This indicates to requesting ITRs
that the Map-Reply was not originated by a LISP node managed at
the site that owns the EID-prefix.
Map-Version Number: When this 12-bit value is non-zero the Map-Reply
sender is informing the ITR what the version number is for the
EID-record contained in the Map-Reply. The ETR can allocate this
number internally but MUST coordinate this value with other ETRs
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for the site. When this value is 0, there is no versioning
information conveyed. The Map-Version Number can be included in
Map-Request and Map-Register messages. See Section 6.5.3 for more
details.
EID-AFI: Address family of EID-prefix according to [RFC5226].
EID-prefix: 4 bytes if an IPv4 address-family, 16 bytes if an IPv6
address-family.
Priority: each RLOC is assigned a unicast priority. Lower values
are more preferable. When multiple RLOCs have the same priority,
they may be used in a load-split fashion. A value of 255 means
the RLOC MUST NOT be used for unicast forwarding.
Weight: when priorities are the same for multiple RLOCs, the weight
indicates how to balance unicast traffic between them. Weight is
encoded as a percentage of total unicast packets that match the
mapping entry. If a non-zero weight value is used for any RLOC,
then all RLOCs MUST use a non-zero weight value and then the sum
of all weight values MUST equal 100. If a zero value is used for
any RLOC weight, then all weights MUST be zero and the receiver of
the Map-Reply will decide how to load-split traffic. See
Section 6.4 for a suggested hash algorithm to distribute load
across locators with same priority and equal weight values. When
a single RLOC exists in a mapping entry, the weight value MUST be
set to 100 and ignored on receipt.
M Priority: each RLOC is assigned a multicast priority used by an
ETR in a receiver multicast site to select an ITR in a source
multicast site for building multicast distribution trees. A value
of 255 means the RLOC MUST NOT be used for joining a multicast
distribution tree.
M Weight: when priorities are the same for multiple RLOCs, the
weight indicates how to balance building multicast distribution
trees across multiple ITRs. The weight is encoded as a percentage
of total number of trees build to the source site identified by
the EID-prefix. If a non-zero weight value is used for any RLOC,
then all RLOCs MUST use a non-zero weight value and then the sum
of all weight values MUST equal 100. If a zero value is used for
any RLOC weight, then all weights MUST be zero and the receiver of
the Map-Reply will decide how to distribute multicast state across
ITRs.
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Unused Flags: set to 0 when sending and ignored on receipt.
L: when this bit is set, the locator is flagged as a local locator to
the ETR that is sending the Map-Reply. When a Map-Server is doing
proxy Map-Replying [LISP-MS] for a LISP site, the L bit is set to
0 for all locators in this locator-set.
p: when this bit is set, an ETR informs the RLOC-probing ITR that the
locator address, for which this bit is set, is the one being RLOC-
probed and may be different from the source address of the Map-
Reply. An ITR that RLOC-probes a particular locator, MUST use
this locator for retrieving the data structure used to store the
fact that the locator is reachable. The "p" bit is set for a
single locator in the same locator set. If an implementation sets
more than one "p" bit erroneously, the receiver of the Map-Reply
MUST select the first locator. The "p" bit MUST NOT be set for
locator-set records sent in Map-Request and Map-Register messages.
R: when this bit is set, the locator is known to be reachable from
the Map-Reply sender's perspective.
Locator: an IPv4 or IPv6 address (as encoded by the 'Loc-AFI' field)
assigned to an ETR or router acting as a proxy replier for the
EID-prefix. Note that the destination RLOC address MAY be an
anycast address. A source RLOC can be an anycast address as well.
The source or destination RLOC MUST NOT be the broadcast address
(255.255.255.255 or any subnet broadcast address known to the
router), and MUST NOT be a link-local multicast address. The
source RLOC MUST NOT be a multicast address. The destination RLOC
SHOULD be a multicast address if it is being mapped from a
multicast destination EID.
Mapping Protocol Data: See [CONS] or [ALT] for details. This field
is optional and present when the UDP length indicates there is
enough space in the packet to include it.
6.1.5. EID-to-RLOC UDP Map-Reply Message
When a Data Probe packet or a Map-Request triggers a Map-Reply to be
sent, the RLOCs associated with the EID-prefix matched by the EID in
the original packet destination IP address field will be returned.
The RLOCs in the Map-Reply are the globally-routable IP addresses of
the ETR but are not necessarily reachable; separate testing of
reachability is required.
Note that a Map-Reply may contain different EID-prefix granularity
(prefix + length) than the Map-Request which triggers it. This might
occur if a Map-Request were for a prefix that had been returned by an
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earlier Map-Reply. In such a case, the requester updates its cache
with the new prefix information and granularity. For example, a
requester with two cached EID-prefixes that are covered by a Map-
Reply containing one, less-specific prefix, replaces the entry with
the less-specific EID-prefix. Note that the reverse, replacement of
one less-specific prefix with multiple more-specific prefixes, can
also occur but not by removing the less-specific prefix rather by
adding the more-specific prefixes which during a lookup will override
the less-specific prefix.
When an ETR is configured with overlapping EID-prefixes, a Map-
Request with an EID that longest matches any EID-prefix MUST be
returned in a single Map-Reply message. For instance, if an ETR had
database mapping entries for EID-prefixes:
10.0.0.0/8
10.1.0.0/16
10.1.1.0/24
10.1.2.0/24
A Map-Request for EID 10.1.1.1 would cause a Map-Reply with a record
count of 1 to be returned with a mapping record EID-prefix of
10.1.1.0/24.
A Map-Request for EID 10.1.5.5, would cause a Map-Reply with a record
count of 3 to be returned with mapping records for EID-prefixes
10.1.0.0/16, 10.1.1.0/24, and 10.1.2.0/24.
Note that not all overlapping EID-prefixes need to be returned, only
the more specifics (note in the second example above 10.0.0.0/8 was
not returned for requesting EID 10.1.5.5) entries for the matching
EID-prefix of the requesting EID. When more than one EID-prefix is
returned, all SHOULD use the same Time-to-Live value so they can all
time out at the same time. When a more specific EID-prefix is
received later, its Time-to-Live value in the Map-Reply record can be
stored even when other less specifics exist. When a a less specific
EID-prefix is received later, its map-cache expiration time SHOULD be
set to the minimum expiration time of any more specific EID-prefix in
the map-cache.
Map-Replies SHOULD be sent for an EID-prefix no more often than once
per second to the same requesting router. For scalability, it is
expected that aggregation of EID addresses into EID-prefixes will
allow one Map-Reply to satisfy a mapping for the EID addresses in the
prefix range thereby reducing the number of Map-Request messages.
Map-Reply records can have an empty locator-set. This type of a Map-
Reply is called a Negative Map-Reply. Negative Map-Replies convey
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special actions by the sender to the ITR or PTR which have solicited
the Map-Reply. There are two primary applications for Negative Map-
Replies. The first is for a Map-Resolver to instruct an ITR or PTR
when a destination is for a LISP site versus a non-LISP site. And
the other is to source quench Map-Requests which are sent for non-
allocated EIDs.
For each Map-Reply record, the list of locators in a locator-set MUST
appear in the same order for each ETR that originates a Map-Reply
message. The locator-set MUST be sorted in order of ascending IP
address where an IPv4 locator address is considered numerically 'less
than' an IPv6 locator address.
When sending a Map-Reply message, the destination address is copied
from the one of the ITR-RLOC fields from the Map-Request. The ETR
can choose a locator address from one of the address families it
supports. For Data-Probes, the destination address of the Map-Reply
is copied from the source address of the Data-Probe message which is
invoking the reply. The source address of the Map-Reply is one of
the local locator addresses listed in the locator-set of any mapping
record in the message and SHOULD be chosen to allow uRPF checks to
succeed in the upstream service provider. The destination port of a
Map-Reply message is copied from the source port of the Map-Request
or Data-Probe and the source port of the Map-Reply message is set to
the well-known UDP port 4342.
6.1.5.1. Traffic Redirection with Coarse EID-Prefixes
When an ETR is misconfigured or compromised, it could return coarse
EID-prefixes in Map-Reply messages it sends. The EID-prefix could
cover EID-prefixes which are allocated to other sites redirecting
their traffic to the locators of the compromised site.
To solve this problem, there are two basic solutions that could be
used. The first is to have Map-Servers proxy-map-reply on behalf of
ETRs so their registered EID-prefixes are the ones returned in Map-
Replies. Since the interaction between an ETR and Map-Server is
secured with shared-keys, it is more difficult for an ETR to
misbehave. The second solution is to have ITRs and PTRs cache EID-
prefixes with mask-lengths that are greater than or equal to a
configured prefix length. This limits the damage to a specific width
of any EID-prefix advertised, but needs to be coordinated with the
allocation of site prefixes. These solutions can be used
independently or at the same time.
At the time of this writing, other approaches are being considered
and researched.
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Type: 3 (Map-Register)
P: This is the proxy-map-reply bit, when set to 1 an ETR sends a Map-
Register message requesting for the Map-Server to proxy Map-Reply.
The Map-Server will send non-authoritative Map-Replies on behalf
of the ETR. Details on this usage will be provided in a future
version of this draft.
Reserved: Set to 0 on transmission and ignored on receipt.
Record Count: The number of records in this Map-Register message. A
record is comprised of that portion of the packet labeled 'Record'
above and occurs the number of times equal to Record count.
Nonce: This 8-byte Nonce field is set to 0 in Map-Register messages.
Key ID: A configured ID to find the configured Message
Authentication Code (MAC) algorithm and key value used for the
authentication function.
Authentication Data Length: The length in bytes of the
Authentication Data field that follows this field. The length of
the the Authentication Data field is dependent on the Message
Authentication Code (MAC) algorithm used. The length field allows
a device that doesn't know the MAC algorithm to correctly parse
the packet.
Authentication Data: The message digest used from the output of the
Message Authentication Code (MAC) algorithm. The entire Map-
Register payload is authenticated with this field preset to 0.
After the MAC is computed, it is placed in this field.
Implementations of this specification MUST include support for
HMAC-SHA-1-96 [RFC2404] and support for HMAC-SHA-128-256 [RFC4634]
is recommended.
The definition of the rest of the Map-Register can be found in the
Map-Reply section. However, the record TTL field is not used and set
to 0.
6.1.7. Encapsulated Control Message Format
An Encapsulated Control Message is used to encapsulate control
packets sent between xTRs and the mapping database system described
in [LISP-MS].
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field MUST be non-zero.
LCM: The format is one of the control message formats described in
this section. At this time, only Map-Request messages and PIM
Join-Prune messages [MLISP] are allowed to be encapsulated.
Encapsulating other types of LISP control messages are for further
study. When Map-Requests are sent for RLOC-probing purposes (i.e
the probe-bit is set), they MUST NOT be sent inside Encapsulated
Control Messages.
6.2. Routing Locator Selection
Both client-side and server-side may need control over the selection
of RLOCs for conversations between them. This control is achieved by
manipulating the Priority and Weight fields in EID-to-RLOC Map-Reply
messages. Alternatively, RLOC information may be gleaned from
received tunneled packets or EID-to-RLOC Map-Request messages.
The following enumerates different scenarios for choosing RLOCs and
the controls that are available:
o Server-side returns one RLOC. Client-side can only use one RLOC.
Server-side has complete control of the selection.
o Server-side returns a list of RLOC where a subset of the list has
the same best priority. Client can only use the subset list
according to the weighting assigned by the server-side. In this
case, the server-side controls both the subset list and load-
splitting across its members. The client-side can use RLOCs
outside of the subset list if it determines that the subset list
is unreachable (unless RLOCs are set to a Priority of 255). Some
sharing of control exists: the server-side determines the
destination RLOC list and load distribution while the client-side
has the option of using alternatives to this list if RLOCs in the
list are unreachable.
o Server-side sets weight of 0 for the RLOC subset list. In this
case, the client-side can choose how the traffic load is spread
across the subset list. Control is shared by the server-side
determining the list and the client determining load distribution.
Again, the client can use alternative RLOCs if the server-provided
list of RLOCs are unreachable.
o Either side (more likely on the server-side ETR) decides not to
send a Map-Request. For example, if the server-side ETR does not
send Map-Requests, it gleans RLOCs from the client-side ITR,
giving the client-side ITR responsibility for bidirectional RLOC
reachability and preferability. Server-side ETR gleaning of the
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client-side ITR RLOC is done by caching the inner header source
EID and the outer header source RLOC of received packets. The
client-side ITR controls how traffic is returned and can alternate
using an outer header source RLOC, which then can be added to the
list the server-side ETR uses to return traffic. Since no
Priority or Weights are provided using this method, the server-
side ETR MUST assume each client-side ITR RLOC uses the same best
Priority with a Weight of zero. In addition, since EID-prefix
encoding cannot be conveyed in data packets, the EID-to-RLOC cache
on tunnel routers can grow to be very large.
o A "gleaned" map-cache entry, one learned from the source RLOC of a
received encapsulated packet, is only stored and used for a few
seconds, pending verification. Verification is performed by
sending a Map-Request to the source EID (the inner header IP
source address) of the received encapsulated packet. A reply to
this "verifying Map-Request" is used to fully populate the map-
cache entry for the "gleaned" EID and is stored and used for the
time indicated from the TTL field of a received Map-Reply. When a
verified map-cache entry is stored, data gleaning no longer occurs
for subsequent packets which have a source EID that matches the
EID-prefix of the verified entry.
RLOCs that appear in EID-to-RLOC Map-Reply messages are assumed to be
reachable when the R-bit for the locator record is set to 1. Neither
the information contained in a Map-Reply or that stored in the
mapping database system provide reachability information for RLOCs.
Such reachability needs to be determined separately, using one or
more of the Routing Locator Reachability Algorithms described in the
next section.
6.3. Routing Locator Reachability
Several mechanisms for determining RLOC reachability are currently
defined:
1. An ETR may examine the Loc-Status-Bits in the LISP header of an
encapsulated data packet received from an ITR. If the ETR is
also acting as an ITR and has traffic to return to the original
ITR site, it can use this status information to help select an
RLOC.
2. An ITR may receive an ICMP Network or ICMP Host Unreachable
message for an RLOC it is using. This indicates that the RLOC is
likely down.
3. An ITR which participates in the global routing system can
determine that an RLOC is down if no BGP RIB route exists that
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matches the RLOC IP address.
4. An ITR may receive an ICMP Port Unreachable message from a
destination host. This occurs if an ITR attempts to use
interworking [INTERWORK] and LISP-encapsulated data is sent to a
non-LISP-capable site.
5. An ITR may receive a Map-Reply from a ETR in response to a
previously sent Map-Request. The RLOC source of the Map-Reply is
likely up since the ETR was able to send the Map-Reply to the
ITR.
6. When an ETR receives an encapsulated packet from an ITR, the
source RLOC from the outer header of the packet is likely up.
7. An ITR/ETR pair can use the Locator Reachability Algorithms
described in this section, namely Echo-Noncing or RLOC-Probing.
When determining Locator up/down reachability by examining the Loc-
Status-Bits from the LISP encapsulated data packet, an ETR will
receive up to date status from an encapsulating ITR about
reachability for all ETRs at the site. CE-based ITRs at the source
site can determine reachability relative to each other using the site
IGP as follows:
o Under normal circumstances, each ITR will advertise a default
route into the site IGP.
o If an ITR fails or if the upstream link to its PE fails, its
default route will either time-out or be withdrawn.
Each ITR can thus observe the presence or lack of a default route
originated by the others to determine the Locator Status Bits it sets
for them.
RLOCs listed in a Map-Reply are numbered with ordinals 0 to n-1. The
Loc-Status-Bits in a LISP encapsulated packet are numbered from 0 to
n-1 starting with the least significant bit. For example, if an RLOC
listed in the 3rd position of the Map-Reply goes down (ordinal value
2), then all ITRs at the site will clear the 3rd least significant
bit (xxxx x0xx) of the Loc-Status-Bits field for the packets they
encapsulate.
When an ETR decapsulates a packet, it will check for any change in
the Loc-Status-Bits field. When a bit goes from 1 to 0, the ETR will
refrain from encapsulating packets to an RLOC that is indicated as
down. It will only resume using that RLOC if the corresponding Loc-
Status-Bit returns to a value of 1. Loc-Status-Bits are associated
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with a locator-set per EID-prefix. Therefore, when a locator becomes
unreachable, the Loc-Status-Bit that corresponds to that locator's
position in the list returned by the last Map-Reply will be set to
zero for that particular EID-prefix.
When ITRs at the site are not deployed in CE routers, the IGP can
still be used to determine the reachability of Locators provided they
are injected into the IGP. This is typically done when a /32 address
is configured on a loopback interface.
When ITRs receive ICMP Network or Host Unreachable messages as a
method to determine unreachability, they will refrain from using
Locators which are described in Locator lists of Map-Replies.
However, using this approach is unreliable because many network
operators turn off generation of ICMP Unreachable messages.
If an ITR does receive an ICMP Network or Host Unreachable message,
it MAY originate its own ICMP Unreachable message destined for the
host that originated the data packet the ITR encapsulated.
Also, BGP-enabled ITRs can unilaterally examine the BGP RIB to see if
a locator address from a locator-set in a mapping entry matches a
prefix. If it does not find one and BGP is running in the Default
Free Zone (DFZ), it can decide to not use the locator even though the
Loc-Status-Bits indicate the locator is up. In this case, the path
from the ITR to the ETR that is assigned the locator is not
available. More details are in [LOC-ID-ARCH].
Optionally, an ITR can send a Map-Request to a Locator and if a Map-
Reply is returned, reachability of the Locator has been determined.
Obviously, sending such probes increases the number of control
messages originated by tunnel routers for active flows, so Locators
are assumed to be reachable when they are advertised.
This assumption does create a dependency: Locator unreachability is
detected by the receipt of ICMP Host Unreachable messages. When an
Locator has been determined to be unreachable, it is not used for
active traffic; this is the same as if it were listed in a Map-Reply
with priority 255.
The ITR can test the reachability of the unreachable Locator by
sending periodic Requests. Both Requests and Replies MUST be rate-
limited. Locator reachability testing is never done with data
packets since that increases the risk of packet loss for end-to-end
sessions.
When an ETR decapsulates a packet, it knows that it is reachable from
the encapsulating ITR because that is how the packet arrived. In
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most cases, the ETR can also reach the ITR but cannot assume this to
be true due to the possibility of path asymmetry. In the presence of
unidirectional traffic flow from an ITR to an ETR, the ITR SHOULD NOT
use the lack of return traffic as an indication that the ETR is
unreachable. Instead, it MUST use an alternate mechanisms to
determine reachability.
6.3.1. Echo Nonce Algorithm
When data flows bidirectionally between locators from different
sites, a simple mechanism called "nonce echoing" can be used to
determine reachability between an ITR and ETR. When an ITR wants to
solicit a nonce echo, it sets the N and E bits and places a 24-bit
nonce in the LISP header of the next encapsulated data packet.
When this packet is received by the ETR, the encapsulated packet is
forwarded as normal. When the ETR next sends a data packet to the
ITR, it includes the nonce received earlier with the N bit set and E
bit cleared. The ITR sees this "echoed nonce" and knows the path to
and from the ETR is up.
The ITR will set the E-bit and N-bit for every packet it sends while
in echo-nonce-request state. The time the ITR waits to process the
echoed nonce before it determines the path is unreachable is variable
and a choice left for the implementation.
If the ITR is receiving packets from the ETR but does not see the
nonce echoed while being in echo-nonce-request state, then the path
to the ETR is unreachable. This decision may be overridden by other
locator reachability algorithms. Once the ITR determines the path to
the ETR is down it can switch to another locator for that EID-prefix.
Note that "ITR" and "ETR" are relative terms here. Both devices MUST
be implementing both ITR and ETR functionality for the echo nonce
mechanism to operate.
The ITR and ETR may both go into echo-nonce-request state at the same
time. The number of packets sent or the time during which echo nonce
requests are sent is an implementation specific setting. However,
when an ITR is in echo-nonce-request state, it can echo the ETR's
nonce in the next set of packets that it encapsulates and then
subsequently, continue sending echo-nonce-request packets.
This mechanism does not completely solve the forward path
reachability problem as traffic may be unidirectional. That is, the
ETR receiving traffic at a site may not be the same device as an ITR
which transmits traffic from that site or the site to site traffic is
unidirectional so there is no ITR returning traffic.
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The echo-nonce algorithm is bilateral. That is, if one side sets the
E-bit and the other side is not enabled for echo-noncing, then the
echoing of the nonce does not occur and the requesting side may
regard the locator unreachable erroneously. An ITR SHOULD only set
the E-bit in a encapsulated data packet when it knows the ETR is
enabled for echo-noncing. This is conveyed by the E-bit in the Map-
Reply message.
Note that other locator reachability mechanisms are being researched
and can be used to compliment or even override the Echo Nonce
Algorithm. See next section for an example of control-plane probing.
6.3.2. RLOC Probing Algorithm
RLOC Probing is a method that an ITR or PTR can use to determine the
reachability status of one or more locators that it has cached in a
map-cache entry. The probe-bit of the Map-Request and Map-Reply
messages are used for RLOC Probing.
RLOC probing is done in the control-plane on a timer basis where an
ITR or PTR will originate a Map-Request destined to a locator address
from one of its own locator addresses. A Map-Request used as an
RLOC-probe is NOT encapsulated and NOT sent to a Map-Server or on the
ALT like one would when soliciting mapping data. The EID record
encoded in the Map-Request is the EID-prefix of the map-cache entry
cached by the ITR or PTR. The ITR or PTR may include a mapping data
record for its own database mapping information.
When an ETR receives a Map-Request message with the probe-bit set, it
returns a Map-Reply with the probe-bit set. The source address of
the Map-Reply is set from the destination address of the Map-Request
and the destination address of the Map-Reply is set from the source
address of the Map-Request. The Map-Reply SHOULD contain mapping
data for the EID-prefix contained in the Map-Request. This provides
the opportunity for the ITR or PTR, which sent the RLOC-probe to get
mapping updates if there were changes to the ETR's database mapping
entries.
There are advantages and disadvantages of RLOC Probing. The greatest
benefit of RLOC Probing is that it can handle many failure scenarios
allowing the ITR to determine when the path to a specific locator is
reachable or has become unreachable, thus providing a robust
mechanism for switching to using another locator from the cached
locator. RLOC Probing can also provide rough RTT estimates between a
pair of locators which can be useful for network management purposes
as well as for selecting low delay paths. The major disadvantage of
RLOC Probing is in the number of control messages required and the
amount of bandwidth used to obtain those benefits, especially if the
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requirement for failure detection times are very small.
Continued research and testing will attempt to characterize the
tradeoffs of failure detection times versus message overhead.
6.4. Routing Locator Hashing
When an ETR provides an EID-to-RLOC mapping in a Map-Reply message to
a requesting ITR, the locator-set for the EID-prefix may contain
different priority values for each locator address. When more than
one best priority locator exists, the ITR can decide how to load
share traffic against the corresponding locators.
The following hash algorithm may be used by an ITR to select a
locator for a packet destined to an EID for the EID-to-RLOC mapping:
1. Either a source and destination address hash can be used or the
traditional 5-tuple hash which includes the source and
destination addresses, source and destination TCP, UDP, or SCTP
port numbers and the IP protocol number field or IPv6 next-
protocol fields of a packet a host originates from within a LISP
site. When a packet is not a TCP, UDP, or SCTP packet, the
source and destination addresses only from the header are used to
compute the hash.
2. Take the hash value and divide it by the number of locators
stored in the locator-set for the EID-to-RLOC mapping.
3. The remainder will be yield a value of 0 to "number of locators
minus 1". Use the remainder to select the locator in the
locator-set.
Note that when a packet is LISP encapsulated, the source port number
in the outer UDP header needs to be set. Selecting a random value
allows core routers which are attached to Link Aggregation Groups
(LAGs) to load-split the encapsulated packets across member links of
such LAGs. Otherwise, core routers would see a single flow, since
packets have a source address of the ITR, for packets which are
originated by different EIDs at the source site. A suggested setting
for the source port number computed by an ITR is a 5-tuple hash
function on the inner header, as described above.
Many core router implementations use a 5-tuple hash to decide how to
balance packet load across members of a LAG. The 5-tuple hash
includes the source and destination addresses of the packet and the
source and destination ports when the protocol number in the packet
is TCP or UDP. For this reason, UDP encoding is used for LISP
encapsulation.
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Since the LISP architecture uses a caching scheme to retrieve and
store EID-to-RLOC mappings, the only way an ITR can get a more up-to-
date mapping is to re-request the mapping. However, the ITRs do not
know when the mappings change and the ETRs do not keep track of who
requested its mappings. For scalability reasons, we want to maintain
this approach but need to provide a way for ETRs change their
mappings and inform the sites that are currently communicating with
the ETR site using such mappings.
When a locator record is added to the end of a locator-set, it is
easy to update mappings. We assume new mappings will maintain the
same locator ordering as the old mapping but just have new locators
appended to the end of the list. So some ITRs can have a new mapping
while other ITRs have only an old mapping that is used until they
time out. When an ITR has only an old mapping but detects bits set
in the loc-status-bits that correspond to locators beyond the list it
has cached, it simply ignores them. However, this can only happen
for locator addresses that are lexicographically greater than the
locator addresses in the existing locator-set.
When a locator record is removed from a locator-set, ITRs that have
the mapping cached will not use the removed locator because the xTRs
will set the loc-status-bit to 0. So even if the locator is in the
list, it will not be used. For new mapping requests, the xTRs can
set the locator AFI to 0 (indicating an unspecified address), as well
as setting the corresponding loc-status-bit to 0. This forces ITRs
with old or new mappings to avoid using the removed locator.
If many changes occur to a mapping over a long period of time, one
will find empty record slots in the middle of the locator-set and new
records appended to the locator-set. At some point, it would be
useful to compact the locator-set so the loc-status-bit settings can
be efficiently packed.
We propose here three approaches for locator-set compaction, one
operational and two protocol mechanisms. The operational approach
uses a clock sweep method. The protocol approaches use the concept
of Solicit-Map-Requests and Map-Versioning.
6.5.1. Clock Sweep
The clock sweep approach uses planning in advance and the use of
count-down TTLs to time out mappings that have already been cached.
The default setting for an EID-to-RLOC mapping TTL is 24 hours. So
there is a 24 hour window to time out old mappings. The following
clock sweep procedure is used:
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1. 24 hours before a mapping change is to take effect, a network
administrator configures the ETRs at a site to start the clock
sweep window.
2. During the clock sweep window, ETRs continue to send Map-Reply
messages with the current (unchanged) mapping records. The TTL
for these mappings is set to 1 hour.
3. 24 hours later, all previous cache entries will have timed out,
and any active cache entries will time out within 1 hour. During
this 1 hour window the ETRs continue to send Map-Reply messages
with the current (unchanged) mapping records with the TTL set to
1 minute.
4. At the end of the 1 hour window, the ETRs will send Map-Reply
messages with the new (changed) mapping records. So any active
caches can get the new mapping contents right away if not cached,
or in 1 minute if they had the mapping cached.
6.5.2. Solicit-Map-Request (SMR)
Soliciting a Map-Request is a selective way for xTRs, at the site
where mappings change, to control the rate they receive requests for
Map-Reply messages. SMRs are also used to tell remote ITRs to update
the mappings they have cached.
Since the xTRs don't keep track of remote ITRs that have cached their
mappings, they can not tell exactly who needs the new mapping
entries. So an xTR will solicit Map-Requests from sites it is
currently sending encapsulated data to, and only from those sites.
The xTRs can locally decide the algorithm for how often and to how
many sites it sends SMR messages.
An SMR message is simply a bit set in a Map-Request message. An ITR
or PTR will send a Map-Request when they receive an SMR message.
Both the SMR sender and the Map-Request responder MUST rate-limited
these messages.
The following procedure shows how a SMR exchange occurs when a site
is doing locator-set compaction for an EID-to-RLOC mapping:
1. When the database mappings in an ETR change, the ETRs at the site
begin to send Map-Requests with the SMR bit set for each locator
in each map-cache entry the ETR caches.
2. A remote xTR which receives the SMR message will schedule sending
a Map-Request message to the source locator address of the SMR
message. A newly allocated random nonce is selected and the EID-
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prefix used is the one copied from the SMR message.
3. The remote xTR MUST rate-limit the Map-Request until it gets a
Map-Reply while continuing to use the cached mapping.
4. The ETRs at the site with the changed mapping will reply to the
Map-Request with a Map-Reply message provided the Map-Request
nonce matches the nonce from the SMR. The Map-Reply messages
SHOULD be rate limited. This is important to avoid Map-Reply
implosion.
5. The ETRs, at the site with the changed mapping, record the fact
that the site that sent the Map-Request has received the new
mapping data in the mapping cache entry for the remote site so
the loc-status-bits are reflective of the new mapping for packets
going to the remote site. The ETR then stops sending SMR
messages.
For security reasons an ITR MUST NOT process unsolicited Map-Replies.
The nonce MUST be carried from SMR packet, into the resultant Map-
Request, and then into Map-Reply to reduce spoofing attacks.
To avoid map-cache entry corruption by a third-party, a sender of an
SMR-based Map-Request MUST be verified. If an ITR receives an SMR-
based Map-Request and the source is not in the locator-set for the
stored map-cache entry, then the responding Map-Request MUST be sent
with an EID destination to the mapping database system. Since the
mapping database system is more secure to reach an authoritative ETR,
it will deliver the Map-Request to the authoritative source of the
mapping data.
6.5.3. Database Map Versioning
When there is unidirectional packet flow between an ITR and ETR, and
the EID-to-RLOC mappings change on the ETR, it needs to inform the
ITR so encapsulation can stop to a removed locator and start to a new
locator in the locator-set.
An ETR, when it sends Map-Reply messages, conveys its own Map-Version
number. This is known as the Destination Map-Version Number. ITRs
include the Destination Map-Version Number in packets they
encapsulate to the site. When an ETR decapsulates a packet and
detects the Destination Map-Version Number is less than the current
version for its mapping, the SMR procedure described in Section 6.5.2
occurs.
An ITR, when it encapsulates packets to ETRs, can convey its own Map-
Version number. This is known as the Source Map-Version Number.
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When an ETR decapsulates a packet and detects the Source Map-Version
Number is greater than the last Map-Version Number sent in a Map-
Reply from the ITR's site, the ETR will send a Map-Request to one of
the ETRs for the source site.
A Map-Version Number is used as a sequence number per EID-prefix. So
values that are greater, are considered to be more recent. A value
of 0 for the Source Map-Version Number or the Destination Map-Version
Number conveys no versioning information and an xTR does no
comparison with previously received Map-Version Numbers.
A Map-Version Number can be included in Map-Register messages as
well. This is a good way for the Map-Server can assure that all ETRs
for a site registering to it will be Map-Version number synchronized.
See [VERSIONING] for a more detailed analysis and description of
Database Map Versioning.
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Internet-Draft Locator/ID Separation Protocol (LISP) April 20107. Router Performance Considerations
LISP is designed to be very hardware-based forwarding friendly. By
doing tunnel header prepending [RFC1955] and stripping instead of re-
writing addresses, existing hardware can support the forwarding model
with little or no modification. Where modifications are required,
they should be limited to re-programming existing hardware rather
than requiring expensive design changes to hard-coded algorithms in
silicon.
A few implementation techniques can be used to incrementally
implement LISP:
o When a tunnel encapsulated packet is received by an ETR, the outer
destination address may not be the address of the router. This
makes it challenging for the control plane to get packets from the
hardware. This may be mitigated by creating special FIB entries
for the EID-prefixes of EIDs served by the ETR (those for which
the router provides an RLOC translation). These FIB entries are
marked with a flag indicating that control plane processing should
be performed. The forwarding logic of testing for particular IP
protocol number value is not necessary. No changes to existing,
deployed hardware should be needed to support this.
o On an ITR, prepending a new IP header is as simple as adding more
bytes to a MAC rewrite string and prepending the string as part of
the outgoing encapsulation procedure. Many routers that support
GRE tunneling [RFC2784] or 6to4 tunneling [RFC3056] can already
support this action.
o When a received packet's outer destination address contains an EID
which is not intended to be forwarded on the routable topology
(i.e. LISP 1.5), the source address of a data packet or the
router interface with which the source is associated (the
interface from which it was received) can be associated with a VRF
(Virtual Routing/Forwarding), in which a different (i.e. non-
congruent) topology can be used to find EID-to-RLOC mappings.
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Internet-Draft Locator/ID Separation Protocol (LISP) April 20108. Deployment Scenarios
This section will explore how and where ITRs and ETRs can be deployed
and will discuss the pros and cons of each deployment scenario.
There are two basic deployment trade-offs to consider: centralized
versus distributed caches and flat, recursive, or re-encapsulating
tunneling.
When deciding on centralized versus distributed caching, the
following issues should be considered:
o Are the tunnel routers spread out so that the caches are spread
across all the memories of each router?
o Should management "touch points" be minimized by choosing few
tunnel routers, just enough for redundancy?
o In general, using more ITRs doesn't increase management load,
since caches are built and stored dynamically. On the other hand,
more ETRs does require more management since EID-prefix-to-RLOC
mappings need to be explicitly configured.
When deciding on flat, recursive, or re-encapsulation tunneling, the
following issues should be considered:
o Flat tunneling implements a single tunnel between source site and
destination site. This generally offers better paths between
sources and destinations with a single tunnel path.
o Recursive tunneling is when tunneled traffic is again further
encapsulated in another tunnel, either to implement VPNs or to
perform Traffic Engineering. When doing VPN-based tunneling, the
site has some control since the site is prepending a new tunnel
header. In the case of TE-based tunneling, the site may have
control if it is prepending a new tunnel header, but if the site's
ISP is doing the TE, then the site has no control. Recursive
tunneling generally will result in suboptimal paths but at the
benefit of steering traffic to resource available parts of the
network.
o The technique of re-encapsulation ensures that packets only
require one tunnel header. So if a packet needs to be rerouted,
it is first decapsulated by the ETR and then re-encapsulated with
a new tunnel header using a new RLOC.
The next sub-sections will describe where tunnel routers can reside
in the network.
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Internet-Draft Locator/ID Separation Protocol (LISP) April 20108.1. First-hop/Last-hop Tunnel Routers
By locating tunnel routers close to hosts, the EID-prefix set is at
the granularity of an IP subnet. So at the expense of more EID-
prefix-to-RLOC sets for the site, the caches in each tunnel router
can remain relatively small. But caches always depend on the number
of non-aggregated EID destination flows active through these tunnel
routers.
With more tunnel routers doing encapsulation, the increase in control
traffic grows as well: since the EID-granularity is greater, more
Map-Requests and Map-Replies are traveling between more routers.
The advantage of placing the caches and databases at these stub
routers is that the products deployed in this part of the network
have better price-memory ratios then their core router counterparts.
Memory is typically less expensive in these devices and fewer routes
are stored (only IGP routes). These devices tend to have excess
capacity, both for forwarding and routing state.
LISP functionality can also be deployed in edge switches. These
devices generally have layer-2 ports facing hosts and layer-3 ports
facing the Internet. Spare capacity is also often available in these
devices as well.
8.2. Border/Edge Tunnel Routers
Using customer-edge (CE) routers for tunnel endpoints allows the EID
space associated with a site to be reachable via a small set of RLOCs
assigned to the CE routers for that site.
This offers the opposite benefit of the first-hop/last-hop tunnel
router scenario: the number of mapping entries and network management
touch points are reduced, allowing better scaling.
One disadvantage is that less of the network's resources are used to
reach host endpoints thereby centralizing the point-of-failure domain
and creating network choke points at the CE router.
Note that more than one CE router at a site can be configured with
the same IP address. In this case an RLOC is an anycast address.
This allows resilience between the CE routers. That is, if a CE
router fails, traffic is automatically routed to the other routers
using the same anycast address. However, this comes with the
disadvantage where the site cannot control the entrance point when
the anycast route is advertised out from all border routers.
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Internet-Draft Locator/ID Separation Protocol (LISP) April 20108.3. ISP Provider-Edge (PE) Tunnel Routers
Use of ISP PE routers as tunnel endpoint routers gives an ISP control
over the location of the egress tunnel endpoints. That is, the ISP
can decide if the tunnel endpoints are in the destination site (in
either CE routers or last-hop routers within a site) or at other PE
edges. The advantage of this case is that two or more tunnel headers
can be avoided. By having the PE be the first router on the path to
encapsulate, it can choose a TE path first, and the ETR can
decapsulate and re-encapsulate for a tunnel to the destination end
site.
An obvious disadvantage is that the end site has no control over
where its packets flow or the RLOCs used.
As mentioned in earlier sections a combination of these scenarios is
possible at the expense of extra packet header overhead, if both site
and provider want control, then recursive or re-encapsulating tunnels
are used.
8.4. LISP Functionality with Conventional NATs
LISP routers can be deployed behind Network Address Translator (NAT)
devices to provide the same set of packet services hosts have today
when they are addressed out of private address space.
It is important to note that a locator address in any LISP control
message MUST be a globally routable address and therefore SHOULD NOT
contain [RFC1918] addresses. If a LISP router is configured with
private addresses, they MUST be used only in the outer IP header so
the NAT device can translate properly. Otherwise, EID addresses MUST
be translated before encapsulation is performed. Both NAT
translation and LISP encapsulation functions could be co-located in
the same device.
More details on LISP address translation can be found in [INTERWORK].
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Internet-Draft Locator/ID Separation Protocol (LISP) April 20109. Traceroute Considerations
When a source host in a LISP site initiates a traceroute to a
destination host in another LISP site, it is highly desirable for it
to see the entire path. Since packets are encapsulated from ITR to
ETR, the hop across the tunnel could be viewed as a single hop.
However, LISP traceroute will provide the entire path so the user can
see 3 distinct segments of the path from a source LISP host to a
destination LISP host:
Segment 1 (in source LISP site based on EIDs):
source-host ---> first-hop ... next-hop ---> ITR
Segment 2 (in the core network based on RLOCs):
ITR ---> next-hop ... next-hop ---> ETR
Segment 3 (in the destination LISP site based on EIDs):
ETR ---> next-hop ... last-hop ---> destination-host
For segment 1 of the path, ICMP Time Exceeded messages are returned
in the normal matter as they are today. The ITR performs a TTL
decrement and test for 0 before encapsulating. So the ITR hop is
seen by the traceroute source has an EID address (the address of
site-facing interface).
For segment 2 of the path, ICMP Time Exceeded messages are returned
to the ITR because the TTL decrement to 0 is done on the outer
header, so the destination of the ICMP messages are to the ITR RLOC
address, the source RLOC address of the encapsulated traceroute
packet. The ITR looks inside of the ICMP payload to inspect the
traceroute source so it can return the ICMP message to the address of
the traceroute client as well as retaining the core router IP address
in the ICMP message. This is so the traceroute client can display
the core router address (the RLOC address) in the traceroute output.
The ETR returns its RLOC address and responds to the TTL decrement to
0 like the previous core routers did.
For segment 3, the next-hop router downstream from the ETR will be
decrementing the TTL for the packet that was encapsulated, sent into
the core, decapsulated by the ETR, and forwarded because it isn't the
final destination. If the TTL is decremented to 0, any router on the
path to the destination of the traceroute, including the next-hop
router or destination, will send an ICMP Time Exceeded message to the
source EID of the traceroute client. The ICMP message will be
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encapsulated by the local ITR and sent back to the ETR in the
originated traceroute source site, where the packet will be delivered
to the host.
9.1. IPv6 Traceroute
IPv6 traceroute follows the procedure described above since the
entire traceroute data packet is included in ICMP Time Exceeded
message payload. Therefore, only the ITR needs to pay special
attention for forwarding ICMP messages back to the traceroute source.
9.2. IPv4 Traceroute
For IPv4 traceroute, we cannot follow the above procedure since IPv4
ICMP Time Exceeded messages only include the invoking IP header and 8
bytes that follow the IP header. Therefore, when a core router sends
an IPv4 Time Exceeded message to an ITR, all the ITR has in the ICMP
payload is the encapsulated header it prepended followed by a UDP
header. The original invoking IP header, and therefore the identity
of the traceroute source is lost.
The solution we propose to solve this problem is to cache traceroute
IPv4 headers in the ITR and to match them up with corresponding IPv4
Time Exceeded messages received from core routers and the ETR. The
ITR will use a circular buffer for caching the IPv4 and UDP headers
of traceroute packets. It will select a 16-bit number as a key to
find them later when the IPv4 Time Exceeded messages are received.
When an ITR encapsulates an IPv4 traceroute packet, it will use the
16-bit number as the UDP source port in the encapsulating header.
When the ICMP Time Exceeded message is returned to the ITR, the UDP
header of the encapsulating header is present in the ICMP payload
thereby allowing the ITR to find the cached headers for the
traceroute source. The ITR puts the cached headers in the payload
and sends the ICMP Time Exceeded message to the traceroute source
retaining the source address of the original ICMP Time Exceeded
message (a core router or the ETR of the site of the traceroute
destination).
The signature of a traceroute packet comes in two forms. The first
form is encoded as a UDP message where the destination port is
inspected for a range of values. The second form is encoded as an
ICMP message where the IP identification field is inspected for a
well-known value.
9.3. Traceroute using Mixed Locators
When either an IPv4 traceroute or IPv6 traceroute is originated and
the ITR encapsulates it in the other address family header, you
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cannot get all 3 segments of the traceroute. Segment 2 of the
traceroute can not be conveyed to the traceroute source since it is
expecting addresses from intermediate hops in the same address format
for the type of traceroute it originated. Therefore, in this case,
segment 2 will make the tunnel look like one hop. All the ITR has to
do to make this work is to not copy the inner TTL to the outer,
encapsulating header's TTL when a traceroute packet is encapsulated
using an RLOC from a different address family. This will cause no
TTL decrement to 0 to occur in core routers between the ITR and ETR.
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Internet-Draft Locator/ID Separation Protocol (LISP) April 201010. Mobility Considerations
There are several kinds of mobility of which only some might be of
concern to LISP. Essentially they are as follows.
10.1. Site Mobility
A site wishes to change its attachment points to the Internet, and
its LISP Tunnel Routers will have new RLOCs when it changes upstream
providers. Changes in EID-RLOC mappings for sites are expected to be
handled by configuration, outside of the LISP protocol.
10.2. Slow Endpoint Mobility
An individual endpoint wishes to move, but is not concerned about
maintaining session continuity. Renumbering is involved. LISP can
help with the issues surrounding renumbering [RFC4192] [LISA96] by
decoupling the address space used by a site from the address spaces
used by its ISPs. [RFC4984]
10.3. Fast Endpoint Mobility
Fast endpoint mobility occurs when an endpoint moves relatively
rapidly, changing its IP layer network attachment point. Maintenance
of session continuity is a goal. This is where the Mobile IPv4
[RFC3344bis] and Mobile IPv6 [RFC3775] [RFC4866] mechanisms are used,
and primarily where interactions with LISP need to be explored.
The problem is that as an endpoint moves, it may require changes to
the mapping between its EID and a set of RLOCs for its new network
location. When this is added to the overhead of mobile IP binding
updates, some packets might be delayed or dropped.
In IPv4 mobility, when an endpoint is away from home, packets to it
are encapsulated and forwarded via a home agent which resides in the
home area the endpoint's address belongs to. The home agent will
encapsulate and forward packets either directly to the endpoint or to
a foreign agent which resides where the endpoint has moved to.
Packets from the endpoint may be sent directly to the correspondent
node, may be sent via the foreign agent, or may be reverse-tunneled
back to the home agent for delivery to the mobile node. As the
mobile node's EID or available RLOC changes, LISP EID-to-RLOC
mappings are required for communication between the mobile node and
the home agent, whether via foreign agent or not. As a mobile
endpoint changes networks, up to three LISP mapping changes may be
required:
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o The mobile node moves from an old location to a new visited
network location and notifies its home agent that it has done so.
The Mobile IPv4 control packets the mobile node sends pass through
one of the new visited network's ITRs, which needs a EID-RLOC
mapping for the home agent.
o The home agent might not have the EID-RLOC mappings for the mobile
node's "care-of" address or its foreign agent in the new visited
network, in which case it will need to acquire them.
o When packets are sent directly to the correspondent node, it may
be that no traffic has been sent from the new visited network to
the correspondent node's network, and the new visited network's
ITR will need to obtain an EID-RLOC mapping for the correspondent
node's site.
In addition, if the IPv4 endpoint is sending packets from the new
visited network using its original EID, then LISP will need to
perform a route-returnability check on the new EID-RLOC mapping for
that EID.
In IPv6 mobility, packets can flow directly between the mobile node
and the correspondent node in either direction. The mobile node uses
its "care-of" address (EID). In this case, the route-returnability
check would not be needed but one more LISP mapping lookup may be
required instead:
o As above, three mapping changes may be needed for the mobile node
to communicate with its home agent and to send packets to the
correspondent node.
o In addition, another mapping will be needed in the correspondent
node's ITR, in order for the correspondent node to send packets to
the mobile node's "care-of" address (EID) at the new network
location.
When both endpoints are mobile the number of potential mapping
lookups increases accordingly.
As a mobile node moves there are not only mobility state changes in
the mobile node, correspondent node, and home agent, but also state
changes in the ITRs and ETRs for at least some EID-prefixes.
The goal is to support rapid adaptation, with little delay or packet
loss for the entire system. Also IP mobility can be modified to
require fewer mapping changes. In order to increase overall system
performance, there may be a need to reduce the optimization of one
area in order to place fewer demands on another.
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In LISP, one possibility is to "glean" information. When a packet
arrives, the ETR could examine the EID-RLOC mapping and use that
mapping for all outgoing traffic to that EID. It can do this after
performing a route-returnability check, to ensure that the new
network location does have a internal route to that endpoint.
However, this does not cover the case where an ITR (the node assigned
the RLOC) at the mobile-node location has been compromised.
Mobile IP packet exchange is designed for an environment in which all
routing information is disseminated before packets can be forwarded.
In order to allow the Internet to grow to support expected future
use, we are moving to an environment where some information may have
to be obtained after packets are in flight. Modifications to IP
mobility should be considered in order to optimize the behavior of
the overall system. Anything which decreases the number of new EID-
RLOC mappings needed when a node moves, or maintains the validity of
an EID-RLOC mapping for a longer time, is useful.
10.4. Fast Network Mobility
In addition to endpoints, a network can be mobile, possibly changing
xTRs. A "network" can be as small as a single router and as large as
a whole site. This is different from site mobility in that it is
fast and possibly short-lived, but different from endpoint mobility
in that a whole prefix is changing RLOCs. However, the mechanisms
are the same and there is no new overhead in LISP. A map request for
any endpoint will return a binding for the entire mobile prefix.
If mobile networks become a more common occurrence, it may be useful
to revisit the design of the mapping service and allow for dynamic
updates of the database.
The issue of interactions between mobility and LISP needs to be
explored further. Specific improvements to the entire system will
depend on the details of mapping mechanisms. Mapping mechanisms
should be evaluated on how well they support session continuity for
mobile nodes.
10.5. LISP Mobile Node Mobility
A mobile device can use the LISP infrastructure to achieve mobility
by implementing the LISP encapsulation and decapsulation functions
and acting as a simple ITR/ETR. By doing this, such a "LISP mobile
node" can use topologically-independent EID IP addresses that are not
advertised into and do not impose a cost on the global routing
system. These EIDs are maintained at the edges of the mapping system
(in LISP Map-Servers and Map-Resolvers) and are provided on demand to
only the correspondents of the LISP mobile node.
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Internet-Draft Locator/ID Separation Protocol (LISP) April 201011. Multicast Considerations
A multicast group address, as defined in the original Internet
architecture is an identifier of a grouping of topologically
independent receiver host locations. The address encoding itself
does not determine the location of the receiver(s). The multicast
routing protocol, and the network-based state the protocol creates,
determines where the receivers are located.
In the context of LISP, a multicast group address is both an EID and
a Routing Locator. Therefore, no specific semantic or action needs
to be taken for a destination address, as it would appear in an IP
header. Therefore, a group address that appears in an inner IP
header built by a source host will be used as the destination EID.
The outer IP header (the destination Routing Locator address),
prepended by a LISP router, will use the same group address as the
destination Routing Locator.
Having said that, only the source EID and source Routing Locator
needs to be dealt with. Therefore, an ITR merely needs to put its
own IP address in the source Routing Locator field when prepending
the outer IP header. This source Routing Locator address, like any
other Routing Locator address MUST be globally routable.
Therefore, an EID-to-RLOC mapping does not need to be performed by an
ITR when a received data packet is a multicast data packet or when
processing a source-specific Join (either by IGMPv3 or PIM). But the
source Routing Locator is decided by the multicast routing protocol
in a receiver site. That is, an EID to Routing Locator translation
is done at control-time.
Another approach is to have the ITR not encapsulate a multicast
packet and allow the the host built packet to flow into the core even
if the source address is allocated out of the EID namespace. If the
RPF-Vector TLV [RFC5496] is used by PIM in the core, then core
routers can RPF to the ITR (the Locator address which is injected
into core routing) rather than the host source address (the EID
address which is not injected into core routing).
To avoid any EID-based multicast state in the network core, the first
approach is chosen for LISP-Multicast. Details for LISP-Multicast
and Interworking with non-LISP sites is described in specification
[MLISP].
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Internet-Draft Locator/ID Separation Protocol (LISP) April 201012. Security Considerations
It is believed that most of the security mechanisms will be part of
the mapping database service when using control plane procedures for
obtaining EID-to-RLOC mappings. For data plane triggered mappings,
as described in this specification, protection is provided against
ETR spoofing by using Return- Routability mechanisms evidenced by the
use of a 24-bit Nonce field in the LISP encapsulation header and a
64-bit Nonce field in the LISP control message. The nonce, coupled
with the ITR accepting only solicited Map-Replies goes a long way
toward providing decent authentication.
LISP does not rely on a PKI infrastructure or a more heavy weight
authentication system. These systems challenge the scalability of
LISP which was a primary design goal.
DoS attack prevention will depend on implementations rate-limiting
Map-Requests and Map-Replies to the control plane as well as rate-
limiting the number of data-triggered Map-Replies.
To deal with map-cache exhaustion attempts in an ITR/PTR, the
implementation should consider putting a maximum cap on the number of
entries stored with a reserve list for special or frequently accessed
sites. This should be a configuration policy control set by the
network administrator who manages ITRs and PTRs.
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Internet-Draft Locator/ID Separation Protocol (LISP) April 201014. Prototype Plans and Status
The operator community has requested that the IETF take a practical
approach to solving the scaling problems associated with global
routing state growth. This document offers a simple solution which
is intended for use in a pilot program to gain experience in working
on this problem.
The authors hope that publishing this specification will allow the
rapid implementation of multiple vendor prototypes and deployment on
a small scale. Doing this will help the community:
o Decide whether a new EID-to-RLOC mapping database infrastructure
is needed or if a simple, UDP-based, data-triggered approach is
flexible and robust enough.
o Experiment with provider-independent assignment of EIDs while at
the same time decreasing the size of DFZ routing tables through
the use of topologically-aligned, provider-based RLOCs.
o Determine whether multiple levels of tunneling can be used by ISPs
to achieve their Traffic Engineering goals while simultaneously
removing the more specific routes currently injected into the
global routing system for this purpose.
o Experiment with mobility to determine if both acceptable
convergence and session continuity properties can be scalably
implemented to support both individual device roaming and site
service provider changes.
Here is a rough set of milestones:
1. Interoperable implementations have been available since the
beginning of 2009.
2. Continue pilot deployment using LISP-ALT as the database mapping
mechanism.
3. Continue prototyping and studying other database lookup schemes,
be it DNS, DHTs, CONS, ALT, NERD, or other mechanisms.
4. Implement the LISP Multicast draft [MLISP].
5. Implement the LISP Mobile Node draft [LISP-MN].
6. Research more on how policy affects what gets returned in a Map-
Reply from an ETR.
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Internet-Draft Locator/ID Separation Protocol (LISP) April 2010
7. Continue to experiment with mixed locator-sets to understand how
LISP can help the IPv4 to IPv6 transition.
8. Add more robustness to locator reachability between LISP sites.
9. Continue the deployment of Proxy-ETRs (PETRs) for uses like uRPF
avoidance, IPv6 connectivity, and LISP-MN.
As of this writing the following accomplishments have been achieved:
1. A unit- and system-tested software switching implementation has
been completed on cisco NX-OS for this draft for both IPv4 and
IPv6 EIDs using a mixed locator-set of IPv4 and IPv6 locators.
2. A unit- and system-tested software switching implementation on
cisco NX-OS has been completed for draft [ALT].
3. A unit- and system-tested software switching implementation on
cisco NX-OS has been completed for draft [INTERWORK]. Support
for IPv4 translation is provided and PTR support for IPv4 and
IPv6 is provided.
4. The cisco NX-OS implementation supports an experimental
mechanism for slow mobility.
5. There are 5 LISP implementations that exist and the first 4
below have gone through interoperability testing at IETF
Hiroshima, based on the draft-ietf-lisp-05.txt spec:
1. cisco NX-OS
2. OpenLISP
3. LISP-Click
4. ZLisp
5. cisco IOS
6. Dave Meyer, Vince Fuller, Darrel Lewis, Gregg Schudel, Andrew
Partan and the rest of the lisp-beta team continue to test all
the features described above on a dual-stack infrastructure.
7. Darrel Lewis and Dave Meyer have deployed both LISP translation
and LISP PTR support in the pilot network. Point your browser
to http://www.lisp4.net to see translation happening in action
so your non-LISP site can access a web server in a LISP site.
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8. Soon http://www.lisp6.net will work where your IPv6 LISP site
can talk to a IPv6 web server in a LISP site by using mixed
address-family based locators.
9. An public domain implementation of LISP is available. See
[OPENLISP] for details.
10. We have deployed Map-Resolvers and Map-Servers on the LISP pilot
network to gather experience with [LISP-MS]. The first layer of
the architecture are the xTRs which use Map-Servers for EID-
prefix registration and Map-Resolvers for EID-to-RLOC mapping
resolution. The second layer are the Map-Resolvers and Map-
Servers which connect to the ALT BGP peering infrastructure.
And the third layer are ALT-routers which aggregate EID-prefixes
and forward Map-Requests.
11. A cisco IOS implementation is available which currently supports
IPv4 and IPv6 encapsulation and decapsulation features.
12. A LISP router based LIG implementation is supported, deployed,
and used daily to debug and test the LISP pilot network. See
[LIG] for details.
13. A Linux implementation of LIG has been made available and
supported by Dave Meyer. It can be run on any Linux system
which resides in either a LISP site or non-LISP site. See [LIG]
for details. Public domain code can be downloaded from
http://github.com/davidmeyer/lig/tree/master.
14. An experimental implementation has been written for three
locator reachability algorithms. Two are the Echo-Noncing and
RLOC-Probing algorithms which are documented in this
specification. The third is called TCP-counts which will be
documented in future drafts.
15. The LISP pilot network has been converted from using MD5 HMAC
authentication for Map-Register messages to SHA-1 HMAC
authentication. ETRs send with SHA-1 but Map-Servers can
received from either for compatibility purposes.
16. The LISP pilot network is in its 3rd generation. Current
experiments are being performed to test EID-prefix aggregation
at multiple service boundaries as well as deploying models for
the existence of multiple Mapping Service Providers (MSPs).
If interested in writing a LISP implementation, testing any of the
LISP implementations, or want to be part of the LISP pilot program,
please contact lisp@ietf.org.
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Internet-Draft Locator/ID Separation Protocol (LISP) April 2010Appendix A. Acknowledgments
An initial thank you goes to Dave Oran for planting the seeds for the
initial ideas for LISP. His consultation continues to provide value
to the LISP authors.
A special and appreciative thank you goes to Noel Chiappa for
providing architectural impetus over the past decades on separation
of location and identity, as well as detailed review of the LISP
architecture and documents, coupled with enthusiasm for making LISP a
practical and incremental transition for the Internet.
The authors would like to gratefully acknowledge many people who have
contributed discussion and ideas to the making of this proposal.
They include Scott Brim, Andrew Partan, John Zwiebel, Jason Schiller,
Lixia Zhang, Dorian Kim, Peter Schoenmaker, Vijay Gill, Geoff Huston,
David Conrad, Mark Handley, Ron Bonica, Ted Seely, Mark Townsley,
Chris Morrow, Brian Weis, Dave McGrew, Peter Lothberg, Dave Thaler,
Eliot Lear, Shane Amante, Ved Kafle, Olivier Bonaventure, Luigi
Iannone, Robin Whittle, Brian Carpenter, Joel Halpern, Roger
Jorgensen, Ran Atkinson, Stig Venaas, Iljitsch van Beijnum, Roland
Bless, Dana Blair, Bill Lynch, Marc Woolward, Damien Saucez, Damian
Lezama, Attilla De Groot, Parantap Lahiri, David Black, Roque
Gagliano, Isidor Kouvelas, Jesper Skriver, Fred Templin, Margaret
Wasserman, Sam Hartman, Michael Hofling, Pedro Marques, Jari Arkko,
Gregg Schudel, Srinivas Subramanian, Amit Jain, Xu Xiaohu, Dhirendra
Trivedi, Yakov Rekhter, John Scudder, John Drake, and Dimitri
Papadimitriou.
In particular, we would like to thank Dave Meyer for his clever
suggestion for the name "LISP". ;-)
This work originated in the Routing Research Group (RRG) of the IRTF.
The individual submission [LISP-MAIN] was converted into this IETF
LISP working group draft.
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Internet-Draft Locator/ID Separation Protocol (LISP) April 2010Appendix B. Document Change LogB.1. Changes to draft-ietf-lisp-07.txt
o Posted April 2010.
o Added I-bit to data header so LSB field can also be used as an
Instance ID field. When this occurs, the LSB field is reduced to
8-bits (from 32-bits).
o Added V-bit to the data header so the 24-bit nonce field can also
be used for source and destination version numbers.
o Added Map-Version 12-bit value to the EID-record to be used in all
of Map-Request, Map-Reply, and Map-Register messages.
o Added multiple ITR-RLOC fields to the Map-Request packet so an ETR
can decide what address to select for the destination of a Map-
Reply.
o Added L-bit (Local RLOC bit) and p-bit (Probe-Reply RLOC bit) to
the Locator-Set record of an EID-record for a Map-Reply message.
The L-bit indicates which RLOCs in the locator-set are local to
the sender of the message. The P-bit indicates which RLOC is the
source of a RLOC-probe Reply (Map-Reply) message.
o Add reference to the LISP Canonical Address Format [LCAF] draft.
o Made editorial and clarification changes based on comments from
Dhirendra Trivedi.
o Added wordsmithing comments from Joel Halpern on DF=1 setting.
o Add John Zwiebel clarification to Echo Nonce Algorithm section6.3.1.
o Add John Zwiebel comment about expanding on proxy-map-reply bit
for Map-Register messages.
o Add NAT section per Ron Bonica comments.
o Fix IDnits issues per Ron Bonica.
o Added section on Virtualization and Segmentation to explain the
use if the Instance ID field in the data header.
o There are too many P-bits, keep their scope to the packet format
description and refer to them by name every where else in the
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spec.
o Scanned all occurrences of "should", "should not", "must" and
"must not" and uppercased them.
o John Zwiebel offered text for section 4.1 to modernize the
example. Thanks Z!
o Make it more clear in the definition of "EID-to-RLOC Database"
that all ETRs need to have the same database mapping. This
reflects a comment from John Scudder.
o Add a definition "Route-returnability" to the Definition of Terms
section.
o In section 9.2, add text to describe what the signature of
traceroute packets can look like.
o Removed references to Data Probe for introductory example. Data-
probes are still part of the LISP design but not encouraged.
o Added the definition for "LISP site" to the Definition of Terms"
section.
B.2. Changes to draft-ietf-lisp-06.txt
Editorial based changes:
o Posted December 2009.
o Fix typo for flags in LISP data header. Changed from "4" to "5".
o Add text to indicate that Map-Register messages must contain a
computed UDP checksum.
o Add definitions for PITR and PETR.
o Indicate an AFI value of 0 is an unspecified address.
o Indicate that the TTL field of a Map-Register is not used and set
to 0 by the sender. This change makes this spec consistent with
[LISP-MS].
o Change "... yield a packet size of L bytes" to "... yield a packet
size greater than L bytes".
o Clarify section 6.1.5 on what addresses and ports are used in Map-
Reply messages.
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o Clarify that LSBs that go beyond the number of locators do not to
be SMRed when the locator addresses are greater lexicographically
than the locator in the existing locator-set.
o Add Gregg, Srini, and Amit to acknowledgment section.
o Clarify in the definition of a LISP header what is following the
UDP header.
o Clarify "verifying Map-Request" text in section 6.1.3.
o Add Xu Xiaohu to the acknowledgment section for introducing the
problem of overlapping EID-prefixes among multiple sites in an RRG
email message.
Design based changes:
o Use stronger language to have the outer IPv4 header set DF=1 so we
can avoid fragment reassembly in an ETR or PETR. This will also
make IPv4 and IPv6 encapsulation have consistent behavior.
o Map-Requests should not be sent in ECM with the Probe bit is set.
These type of Map-Requests are used as RLOC-probes and are sent
directly to locator addresses in the underlying network.
o Add text in section 6.1.5 about returning all EID-prefixes in a
Map-Reply sent by an ETR when there are overlapping EID-prefixes
configure.
o Add text in a new subsection of section 6.1.5 about dealing with
Map-Replies with coarse EID-prefixes.
B.3. Changes to draft-ietf-lisp-05.txt
o Posted September 2009.
o Added this Document Change Log appendix.
o Added section indicating that encapsulated Map-Requests must use
destination UDP port 4342.
o Don't use AH in Map-Registers. Put key-id, auth-length, and auth-
data in Map-Register payload.
o Added Jari to acknowledgment section.
o State the source-EID is set to 0 when using Map-Requests to
refresh or RLOC-probe.
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o Make more clear what source-RLOC should be for a Map-Request.
o The LISP-CONS authors thought that the Type definitions for CONS
should be removed from this specification.
o Removed nonce from Map-Register message, it wasn't used so no need
for it.
o Clarify what to do for unspecified Action bits for negative Map-
Replies. Since No Action is a drop, make value 0 Drop.
B.4. Changes to draft-ietf-lisp-04.txt
o Posted September 2009.
o How do deal with record count greater than 1 for a Map-Request.
Damien and Joel comment. Joel suggests: 1) Specify that senders
compliant with the current document will always set the count to
1, and note that the count is included for future extensibility.
2) Specify what a receiver compliant with the draft should do if
it receives a request with a count greater than 1. Presumably, it
should send some error back?
o Add Fred Templin in acknowledgment section.
o Add Margaret and Sam to the acknowledgment section for their great
comments.
o Say more about LAGs in the UDP section per Sam Hartman's comment.
o Sam wants to use MAY instead of SHOULD for ignoring checksums on
ETR. From the mailing list: "You'd need to word it as an ITR MAY
send a zero checksum, an ETR MUST accept a 0 checksum and MAY
ignore the checksum completely. And of course we'd need to
confirm that can actually be implemented. In particular, hardware
that verifies UDP checksums on receive needs to be checked to make
sure it permits 0 checksums."
o Margaret wants a reference to
http://www.ietf.org/id/draft-eubanks-chimento-6man-00.txt.
o Fix description in Map-Request section. Where we describe Map-
Reply Record, change "R-bit" to "M-bit".
o Add the mobility bit to Map-Replies. So PTRs don't probe so often
for MNs but often enough to get mapping updates.
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o Indicate SHA1 can be used as well for Map-Registers.
o More Fred comments on MTU handling.
o Isidor comment about spec'ing better periodic Map-Registers. Will
be fixed in draft-ietf-lisp-ms-02.txt.
o Margaret's comment on gleaning: "The current specification does
not make it clear how long gleaned map entries should be retained
in the cache, nor does it make it clear how/ when they will be
validated. The LISP spec should, at the very least, include a
(short) default lifetime for gleaned entries, require that they be
validated within a short period of time, and state that a new
gleaned entry should never overwrite an entry that was obtained
from the mapping system. The security implications of storing
"gleaned" entries should also be explored in detail."
o Add section on RLOC-probing per working group feedback.
o Change "loc-reach-bits" to "loc-status-bits" per comment from
Noel.
o Remove SMR-bit from data-plane. Dino prefers to have it in the
control plane only.
o Change LISP header to allow a "Research Bit" so the Nonce and LSB
fields can be turned off and used for another future purpose. For
Luigi et al versioning convergence.
o Add a N-bit to the data header suggested by Noel. Then the nonce
field could be used when N is not 1.
o Clarify that when E-bit is 0, the nonce field can be an echoed
nonce or a random nonce. Comment from Jesper.
o Indicate when doing data-gleaning that a verifying Map-Request is
sent to the source-EID of the gleaned data packet so we can avoid
map-cache corruption by a 3rd party. Comment from Pedro.
o Indicate that a verifying Map-Request, for accepting mapping data,
should be sent over the the ALT (or to the EID).
o Reference IPsec RFC 4302. Comment from Sam and Brian Weis.
o Put E-bit in Map-Reply to tell ITRs that the ETR supports echo-
noncing. Comment by Pedro and Dino.
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o Jesper made a comment to loosen the language about requiring the
copy of inner TTL to outer TTL since the text to get mixed-AF
traceroute to work would violate the "MUST" clause. Changed from
MUST to SHOULD in section 5.3.
B.5. Changes to draft-ietf-lisp-03.txt
o Posted July 2009.
o Removed loc-reach-bits longword from control packets per Damien
comment.
o Clarifications in MTU text from Roque.
o Added text to indicate that the locator-set be sorted by locator
address from Isidor.
o Clarification text from John Zwiebel in Echo-Nonce section.
B.6. Changes to draft-ietf-lisp-02.txt
o Posted July 2009.
o Encapsulation packet format change to add E-bit and make loc-
reach-bits 32-bits in length.
o Added Echo-Nonce Algorithm section.
o Clarification how ECN bits are copied.
o Moved S-bit in Map-Request.
o Added P-bit in Map-Request and Map-Reply messages to anticipate
RLOC-Probe Algorithm.
o Added to Mobility section to reference draft-meyer-lisp-mn-00.txt.
B.7. Changes to draft-ietf-lisp-01.txt
o Posted 2 days after draft-ietf-lisp-00.txt in May 2009.
o Defined LEID to be a "LISP EID".
o Indicate encapsulation use IPv4 DF=0.
o Added negative Map-Reply messages with drop, native-forward, and
send-map-request actions.
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